World War II was a global military conflict that, in terms of lives lost and material destruction, was the most devastating war in human history. It began in 1939 as a European conflict between Germany and an Anglo-French coalition but eventually widened to include most of the nations of the world. It ended in 1945, leaving a new world order dominated by the United States and the Union of Soviet Socialist Republics (USSR).
More than any previous war, World War II involved the commitment of nations’ entire human and economic resources, the blurring of the distinction between combatant and noncombatant, and the expansion of the battlefield to include all of the enemy’s territory. The most important determinants of its outcome were industrial capacity and personnel. In the last stages of the war, two radically new weapons were introduced: the long-range rocket and the atomic bomb. In the main, however, the war was fought with the same or improved weapons of the types used in World War I (1914-1918). The greatest advances were in aircraft and tanks.

World War I was one of the most devastating war that involves the commitment of nations and resources in the world history. The war was a military conflict, from August 1914 to November 1918, that involved many of the countries of Europe as well as the United States and other nations throughout the world. World War I was one of the most violent and destructive wars in European history. Of the 65 million men who were mobilized, more than 10 million were killed and more than 20 million wounded. The term World War I did not come into general use until a second worldwide conflict broke out in 1939 (see World War II). Before that year, the war was known as the Great War or the World War.

Wars of Yugoslav Succession, armed conflicts within the former Socialist Federal Republic of Yugoslavia (SFRY) during the 1990s. The SFRY was a federation that consisted of six republics—Bosnia and Herzegovina, Croatia, Macedonia (see Former Yugoslav Republic of Macedonia), Montenegro, Serbia, and Slovenia—and multiple nationalities. It broke apart in 1991 and 1992. The conflicts consisted of three wars fought from 1991 to 1995 and a fourth war in 1999. These four struggles have been called the wars of Yugoslav succession because they determined what countries succeeded the SFRY.

War of 1812, conflict between the United States and Britain that began in 1812 and lasted until early 1815. President James Madison requested a declaration of war to protect American ships on the high seas and to stop the British from impressing or seizing U.S. sailors. U.S. ships were being stopped and searched by both Great Britain and France, who were fighting each other in Europe. President Madison also wanted to prevent Britain from forming alliances with Native Americans on the American frontier. His decision was influenced by Americans in the West and South, who hoped to expand the United States by seizing control of both Canada and Florida. Critics called the War of 1812 “Mr. Madison’s War,” but others saw it as a “second war of independence,” an opportunity for Americans to defend their freedom and honor in the face of European disrespect. Neither Britain nor the United States was particularly well prepared to fight this war, and the conflict eventually ended in a stalemate.

Vietnam War, also known as the Second Indochina War, military struggle fought in Vietnam from 1959 to 1975, involving the North Vietnamese and the National Liberation Front (NLF) in conflict with United States forces and the South Vietnamese army. From 1946 until 1954, the Vietnamese had struggled for their independence from France during the First Indochina War. At the end of this war, the country was temporarily divided into North and South Vietnam. North Vietnam came under the control of Vietnamese Communists who had opposed France and who aimed for a unified Vietnam under Communist rule. The South was controlled by non-Communist Vietnamese.

U.S.-Iraq War, military action begun in 2003 with a United States invasion of Iraq, then ruled by the authoritarian regime of Saddam Hussein. The invasion led to a protracted U.S. occupation of Iraq and the birth of a guerrilla insurgency against the occupation. The resulting destabilization of Iraq also created conditions for a civil war to break out between Iraq’s majority Shia Muslim population and its minority Sunni Muslim population. In addition to attempting to quell the insurgency, U.S. forces also found themselves trying to police the civil war. By 2007 the U.S. war in Iraq had lasted longer than U.S. involvement in World War II.

Trojan War, in Greek legend, famous war waged by the Greeks against the city of Troy. The tradition is believed to reflect a real war between the Greeks of the late Mycenaean period and the inhabitants of the Troad, or Troas, in Anatolia, part of present-day Turkey. Modern archaeological excavations have shown that Troy was destroyed by fire sometime between 1230 bc and 1180 bc, and that the war may have resulted from the desire either to plunder the wealthy city or to put an end to Troy's commercial control of the Dardanelles.

Tet Offensive, military campaign of the Vietnam War (1959-1975), in which almost every major city and province in South Vietnam was attacked by the Communist forces of the National Liberation Front (NLF), with support from the North Vietnamese Peoples’ Army of Vietnam (PAVN). Although the Communist forces failed to hold the cities, the Tet Offensive helped undermine American public support for the U.S military involvement in Vietnam.

Spanish-American War, brief war that the United States waged against Spain in 1898. Actual hostilities in the war lasted less than four months, from April 25 to August 12, 1898. Most of the fighting occurred in or near the Spanish colonial possessions of Cuba and the Philippines, nearly halfway around the world from each other. In both theaters the decisive military event was the complete destruction of a Spanish naval squadron by a vastly superior U.S. fleet. These victories left the Spanish land forces isolated from their homeland and, after brief resistance, brought about their surrender to U.S. military forces. The defeat marked the end of Spain’s colonial empire and the rise of the United States as a global military power.

Persian Gulf War, conflict beginning in August 1990, when Iraqi forces invaded and occupied Kuwait. The conflict culminated in fighting in January and February 1991 between Iraq and an international coalition of forces led by the United States. By the end of the war, the coalition had driven the Iraqis from Kuwait.

Mexican War, conflict between the United States and Mexico, lasting from 1846 to 1848. The war resulted in a decisive U.S. victory and forced Mexico to relinquish all claims to approximately half its national territory. Mexico had already lost control of much of its northeastern territory as a result of the Texas Revolution (1835-1836). This land, combined with the territory Mexico ceded at the end of the war, would form the future U.S. states of Arizona, California, Nevada, New Mexico, Texas, and Utah, as well as portions of the states of Colorado, Kansas, Oklahoma, and Wyoming. See United States (History): War with Mexico.
Mexico’s territorial losses signified the end of any likelihood that Mexico, rather than the United States, would become the predominant power in North America. As the first conflict in which U.S. military forces fought almost exclusively outside of the country, the Mexican War also marked the beginning of the rise of the United States as a global military power.

Korean War, civil and military struggle that was fought on the Korea Peninsula and that reached its height between 1950 and 1953.
The Korean War originated in the division of Korea into South Korea and North Korea after World War II (1939-1945). Efforts to reunify the peninsula after the war failed, and in 1948 the South proclaimed the Republic of Korea and the North established the People’s Republic of Korea. In 1949 border fighting broke out between the North and the South. On June 25, 1950, North Korean forces crossed the dividing line and invaded the South. Soon, in defense of the South, the United States joined the fighting under the banner of the United Nations (UN), along with small contingents of British, Canadian, Australian, and Turkish troops. In October 1950 China joined the war on the North’s side. By the time a cease-fire agreement was signed on July 27, 1953, millions of soldiers and civilians had perished. The armistice ended the fighting, but Korea has remained divided for decades since and subject to the possibility of a new war at any time.

Iran-Iraq War, armed conflict that began when Iraq invaded Iran in September 1980 and ended in August 1988 after both sides accepted a cease-fire sponsored by the United Nations (UN). The war was one of the longest and most destructive of the 20th century, with likely more than one million casualties. Despite the conflict's length and cost, neither Iran nor Iraq made significant territorial or political gains, and the fundamental issues dividing the countries remained unresolved at the end of the war.

Hundred Years’ War, armed conflict between France and England during the years from 1337 to 1453. The Hundred Years’ War was a series of short conflicts, broken intermittently by a number of truces and peace treaties. It resulted from disputes between the ruling families of the two countries, the French Capetians (see Capet) and the English Plantagenets, over territories in France and the succession to the French throne.

French Revolution, major transformation of the society and political system of France, lasting from 1789 to 1799. During the course of the Revolution, France was temporarily transformed from an absolute monarchy, where the king monopolized power, to a republic of theoretically free and equal citizens. The effects of the French Revolution were widespread, both inside and outside of France, and the Revolution ranks as one of the most important events in the history of Europe.

French and Indian War (1754-1763), the last of four North American wars waged from 1689 to 1763 between the British and the French. In these struggles, each country fought for control of the continent with the assistance of Native American and colonial allies. The French and Indian War differed from previous confrontations, however. The earlier wars consisted primarily of skirmishes between small regular units of the European powers aided by local militiamen. The French and Indian War was part of a 'great war for empire,' a determined and eventually successful attempt by the British to attain a dominant position in North America, the West Indies, and the subcontinent of India. Although the French and Indian War began in America, it expanded into Europe as the Seven Years' War (1756-1763), and at the same time into Asia as the Third Carnatic War (see Carnatic Wars). The French and Indian War not only stripped France of its North American empire, it also caused Britain to change its relationship to its colonies, a change that eventually led to the American Revolution.

D-Day Invasion or Invasion of Normandy, the 1944 Allied assault on Nazi-occupied northern Europe that assembled the largest force in the history of amphibious warfare and represented a major turning point in World War II (1939-1945). The Allied forces consisted of 20 U.S. divisions, 14 British divisions, 3 Canadian divisions, a French division, and a Polish division. On the first day of the invasion, June 6, about 120,000 Allied troops landed at five beach locations along the coast of the French province of Normandy after crossing the English Channel from bases in southern England. The Allies faced a force of about 50,000 Germans and suffered nearly 5,000 casualties on the first day alone but succeeded in securing the beaches from which they launched their offensive. Many historians consider the D-Day invasion the greatest military achievement of the 20th century.

Cold War, term used to describe the post-World War II struggle between the United States and its allies and the Union of Soviet Socialist Republics (USSR) and its allies. During the Cold War period, which lasted from the mid-1940s until the end of the 1980s, international politics were heavily shaped by the intense rivalry between these two great blocs of power and the political ideologies they represented: democracy and capitalism in the case of the United States and its allies, and Communism in the case of the Soviet bloc.

Battle of Waterloo, final and decisive action of the Napoleonic Wars, that effectively ended French domination of the European continent and brought about drastic changes in the political boundaries and the power balance of Europe. Fought on June 18, 1815, near Waterloo, in what is now Belgium, the battle ranks as a great turning point in modern history.

Battle of Stalingrad (1942-1943), World War II battle that halted the German advance into the Union of Soviet Socialist Republics (USSR).
The Battle of Stalingrad lasted from August 1942 to February 1943. It involved the German Sixth Army and the Fourth Panzer Army, totaling about 290,000 troops, against the Soviet Red Army led by General Georgy Zhukov and General Aleksandr M. Vasilyevsky. Historians disagree about whether the Battle of Stalingrad was a turning point in World War II (1939-1945), but there is common agreement that after the Soviet victory at Stalingrad (present-day Volgograd), the German army, known as the Wehrmacht, was in retreat until it was driven from Soviet territory.

Battle of Gettysburg, battle fought July 1 through July 3, 1863, considered by most military historians the turning point in the American Civil War. The Battle of Gettysburg was a decisive engagement in that it arrested the Confederates' second and last major invasion of the North, destroyed their offensive strategy, and forced them to fight a defensive war in which the inadequacies of their manufacturing capacity and transportation facilities doomed them to defeat.

Battle of Bunker Hill, first large-scale engagement of the American Revolution, fought on June 17, 1775, in Charlestown (now part of Boston), Massachusetts. At issue in the battle was possession of Bunker Hill (34 m/110 ft) and Breed's Hill (23 m/75 ft), adjoining heights dominating Boston Harbor. About 1200 American troops, led by Colonel William Prescott, occupied and fortified Breed's Hill during the night of June 16 as part of a strategic plan to compel the British to evacuate Boston. After daybreak on June 17 the British commander in chief Thomas Gage began preparations for an attack on the American position. Naval units were brought within shelling range of Breed's Hill and about 2200 troops under the command of General William Howe were dispatched from Boston. Meanwhile, about 300 additional volunteers, including General Joseph Warren, had joined the American force.