The 10 Biggest Wars in U.S. History

We all know war is an ugly aspect of the human race. Millions of people have died throughout history through wars caused by numerous reasons: territory disputes, religious differences, greed. The obvious cost of war is that of human life, but there is also a huge financial burden to bear when countries go to war. Allies can remain indebted to each other for decades after a conflict, for example, in 1945 the USA loaned $4.33 billion to the UK to assist with the costs of World War II. The UK finally finished the loan repayments in 2006, taking 61 years to pay back its wartime ally. The final repayment cost was $7.5 billion.

The US has been involved in many wars since the 18th century, some on its own territory and many in other areas of the globe. The military costs of the wars listed here are based on actual operations. Figures have been adjusted with inflation rates (2011) and obviously some educated estimates have had to be made when expense reports have not been filed. The figure in parenthesis is the estimated cost for the actual period that the war took place in. The list is ranked by the rates adjusted for inflation.

For example, The War of 1812 was an outbreak of hostilities between the USA and UK that actually lasted from 1812 to 1815. The military cost of the war has been estimated at $90 million at the time, but with inflation is boosted to a huge cost of $1.553 billion. This represented 2.7% of the total Gross Domestic Product (GDP) given over for defense during the peak year of the war (1813).

Here, we've looked back as far as 1775 and right up until 2010 to examine which wars were the biggest - as in, the costliest - for America. It's part history lesson, part shocking report on the reality of the cost of war; and that's just economic. For every war on this list, there is of course the tragic, inestimable cost of human lives lost.

10 The Mexican-American War: $2.376 billion ($71 million)

Although this conflict has a lower cost historically than The War of 1812, the estimated military cost of this war between 1846 and 1849 adjusted for inflation is over $2 billion (because the dollar had a higher value in 1847 than 1813). The US government had annexed Texas during this time, much to the annoyance of the Mexican government - which eventually led to war. The hostilities lasted for 21 months and ended with an American victory, with Mexico recognizing Texas' independence. By 1847, defense spending had reached a high of 1.9% of the entire US GDP.

9 The American Revolutionary War: $2.407 billion ($101 million)

This is the celebrated period of history when the USA fought against the British Empire and won. The Revolution lasted from 1765 until 1783, with the American Revolutionary War fought from 1775 until 1783. During the eight years of armed conflict, the USA spent the current equivalent of over $2.4 billion, to win their independence from the British crown. The treaties which formed The Peace of Paris saw an end to the war and allowed the fledgling American nation to grow into the international superpower it is now.

8 The Spanish-American War: $9.034 billion ($283 million)

Although this war only lasted for a few months in 1898, it was hugely expensive. A lot of the cost was due to nature of the conflict, as it was fought in places such as Cuba, Puerto Rico, the Philippines and Guam. The expense represented 1.5% of the country's GDP in 1899, but it did gain the nation some overseas territories - and the attention of the rest of the world.

7 The American Civil War: $79.742 billion ($4.183 billion)

This was an incredibly destructive war that raged throughout the United States from 1861 until 1865. The gargantuan cost can be broken down per side: $59.631 billion spent by the Union, $20.111 billion spent by the Confederacy. This war was crippling financially and had a devastating human cost: 750,000 military deaths makes it the most lethal war in American history in terms of body count. The Battle of Gettysburg alone resulted in nearly 8,000 deaths. By 1865 the war was costing America 11.7% of the GDP.

6 The Gulf War: $102 billion ($61 billion)

Moving into the costly 20th century, the Gulf War of 1990-1991 cost the USA the equivalent of over $100 billion. A coalition came together to remove an invading Iraqi army that had broken international law and occupied Kuwait. Although the operations involved were extremely expensive, Saudi Arabia ended up covering $36 billion of the US's $61 billion military bill, thus easing the burden. However, it still registered a hefty 4.6% of GDP spent in total on defense in 1991 (although the war cost was substantially lower, at 0.3%).

5 World War I: $334 billion ($20 billion)

This is another example of a more valuable historical dollar making the inflated cost greater than a seemingly more expensive war (in this case, the Gulf War). World War I lasted from 1914 to 1918, with the US entering the war and joining the allies in 1917. In that year of involvement in the Great War, the US lost over 100,000 military personnel and was spending 14.1% of its GDP on defense by 1919.

4 The Korean War: $341 billion ($30 billion)

Just beating out World War I is the Korean War of 1950-1953. Often called The Forgotten War, hundreds of thousands of Americans fought on the other side of the world whilst most people were still getting over the incredible destruction of World War II. By 1952, 13.2% of the USA's GDP was being spent on defense, with the world starting to get nervous about an escalation to nuclear war.

3 The Vietnam War: $738 billion ($111 billion)

It's no surprise that this much-publicised conflict is in the higher echelons of this list. Stretching from 1956 until 1975 (with US military operations fully commencing in 1965) this war saw thousands of young Americans shipped off to the Far East, to fight in a landscape that felt alien and was festered with hidden dangers. 9.5% of the GDP was being used for defense by 1968, but the war still ended in a demoralizing defeat for the anti-Communist forces.

2 The War on Terror: $1.147 trillion ($1.046 trillion)

Crossing into trillion-dollar territory is the ongoing War on Terror, which includes the Iraq War (2003-2011) and the War in Afghanistan (2001-present). Taking up 4.3% of the GDP by 2008, this war has seen some spectacular successes for America, as well as painful setbacks. A global coalition has attempted to bring some much-needed security to some of the most turbulent places on the planet, but this war now seems to be stretching on into the interminable distance. Recently, America committed to withdrawing troops from Afghanistan, but this is a process which is set to take years.

1 World War II: $4.104 trillion ($296 billion)

This devastating world war dating from 1939 to 1945 saw the USA entering in 1941 after the attack on Pearl Harbor. In the last year of the war, America was spending 37.5% of her GDP on defense, with a massive 35.8% of GDP classed as war cost. This terrible conflict cost well over 400,000 American lives, with the global tally estimated at anywhere up to 80 million people. However, some analysts estimate that the War on Terror could eventually top $4.4 trillion, meaning it could eventually take the place of the costliest war the US has ever been involved in.

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