The Crimean War (1853–1856)
    The Crimean War was fought between Imperial Russia on one side and an alliance of France, the United Kingdom, the Kingdom of Sardinia, and the Ottoman Empire on the other. Most of the conflict took place on the Crimean Peninsula, with additional actions occurring in western Turkey, and the Baltic Sea region. The Crimean War is sometimes considered to be the first "modern" conflict and "introduced technical changes which affected the future course of warfare. The War brought to a close the era of Anglo-Russian domination in Europe. Great Britain, by fighting with France in the Near East, and Russia, by fighting against France, both conceded equality to her as a Mediterranean power.

The Boer War - South Africa (1899-1902)
    The Second Boer War, commonly referred to as The Boer War and also known as the South African War (outside of South Africa), the Anglo-Boer War (among most South Africans) and in Afrikaans as the Anglo-Boereoorlog or Tweede Vryheidsoorlog ("Second War of Independence"), was fought from 11 October 1899 until 31 May 1902, between the British Empire and the two independent Boer republics of the Orange Free State and the South African Republic (Transvaal Republic). After a protracted, hard-fought war, the two independent republics were absorbed into the British Empire.

World War I (1914-1918)
      The first truly global conflict involving more countries than any war except World War II; also called "The war to end all wars" and "The Great War." The fighting took place mostly in Europe. The Allies included Australia, Great Britain, France, Russia (until 1917), Italy, and the United States (1917-1918). The Central Powers consisted of Germany, Austria-Hungary, Turkey, and Bulgaria. Its causes included extreme nationalism among Europeans, a race for colonial possessions fuelled by imperialism, and economic rivalries. The "Great War" was one of the bloodiest in history--an estimated eight to ten million troops were killed. Nearly as many civilians died from disease, starvation, or other causes.

World War II (1939-1945)
      Global conflict involving every major power in the world. The Allies originally consisted of Great Britain, France, and China, but totalled fifty nations, including the Australia, United States and the Soviet Union, by the end of the war. The Axis powers of Germany, Italy, Japan and (until 1941) the Soviet Union were eventually joined by six other nations. Causes of the war were the rise of imperialist and totalitarian dictatorships in Germany, Italy, and Japan after World War I and a world wide economic collapse, the Great Depression. Military deaths in the worldwide conflict were predictably massive, totalling in excess of 17 million troops. The number of civilian deaths due to bombing raids, starvation, and disease was even greater. When the Allies liberated the death camps in Germany and Poland, they were horrified to discover the extent of the Holocaust that Germany had conducted during the war. Some 12 million people had been murdered, including 6 million Jews. The Soviet Union suffered the most deaths of any single country--about 20 million military personnel and civilians died.

Korean War (1950-1953)
      Conflict pitting South Korea and U.N. forces against North Korea and later the People's Republic of China. The war began when the North Korean Communist army crossed the thirty-eighth parallel on June 25, 1950, invading the Republic of South Korea. The United Nations Security Council, declaring North Korea an aggressor, sent troops to counter the invasion. Sixteen nations sent troops, and forty-one countries sent food and supplies, but the United States was the largest contributor of arms, troops and equipment. The war reached a stalemate in June, 1951, and after two years of negotiations an armistice was signed July 27, 1953, with the thirty-eighth parallel designated as the border between North and South Korea.

Vietnamese War (1955-1975)
      Military conflict in Vietnam between the U.S.-backed South Vietnamese government and the Communist-led guerrilla forces backed by North Vietnam. The war, the nation's longest, resulted in the loss of 56,121 American lives and was the first in which the United States failed to achieve its goals. The tonnage of bombs dropped on North Vietnam by the United States was greater than the total of that dropped on Germany, Italy, and Japan during World War II. The war left up to 10 million refugees and caused sharp divisions among the American people.

The Persian Gulf War (1990 - 1991)
      On August 2, 1990, Iraqi forces invaded Kuwait and quickly seized control of the small nation. Within days, the United States, along with the United Nations, demanded Iraq's immediate withdrawal. U.S. and other UN member nations began deploying troops in Saudi Arabia within the week. By January of 1991, over half a million allied troops were deployed in Saudi Arabia and throughout the Gulf region. On 16th January 1991, Allied forces began the devastating bombing of Iraq and her forces in Kuwait. Allied forces launched the ground war on 23rd February. Cut off from their supply bases and headquarters by the intense air campaign, thousands of Iraqi soldiers simply gave up rather than fight, as the Allies pushed through Iraq's defences with relative ease. By 26th February, Allied forces controlled Kuwait City. On 27th February, President Bush ordered a cease-fire and the surviving Iraqi troops were allowed to escape back into southern Iraq. On 3rd March 1991, Iraq accepted the terms of the cease-fire and the fighting ended. Original figures listed 100,000 Iraqi military dead, but more recent estimates place Iraqi dead at 20,000 military and 2,300 civilian. The United States had 148 killed in action, 458 wounded. In addition, 121 Americans died through non-combat incidents.

The Iraq War (2003 - Ongoing)
      The Iraq War (or War in Iraq) began on March 20, 2003 with the invasion of Iraq by the United States under the administration of President George W. Bush and the United Kingdom under Prime Minister Tony Blair. The war is also referred to as the Occupation of Iraq, the Second Gulf War, or Operation Iraqi Freedom by the US military. The invasion of Iraq led to an occupation and the eventual capture of President Saddam, who was later tried in an Iraqi court of law and executed by the new Iraqi government. In June 2008, U.S. Department of Defence officials claimed security and economic indicators began to show signs of improvement in what they hailed as significant and fragile gains. In 2007, Iraq was second on the Failed States Index; though its ranking has steadily improved since then, moving to fifth on the 2008 list, sixth in 2009, and seventh in 2010. As public opinion favouring troop withdrawals increased and as Iraqi forces began to take responsibility for security, member nations of the Coalition withdrew their forces. In late 2008, the U.S. and Iraqi governments approved a Status of Forces Agreement effective through January 1, 2012. The Iraqi Parliament also ratified a Strategic Framework Agreement with the U.S., aimed at ensuring cooperation in constitutional rights, threat deterrence, education, energy development, and other areas. In late February 2009, newly elected U.S. President Barack Obama announced an 18-month withdrawal window for combat forces, with approximately 50,000 troops remaining in the country "to advise and train Iraqi security forces and to provide intelligence and surveillance". However on October 21, 2011, President Obama announced that all U.S. troops and trainers would leave Iraq by the end of the year, bringing the U.S. mission in Iraq to an end.

Current List of people on this site that are known to have done Military Service

For more info: Source; Wikipedia:Lists of wars