Rome spent centuries flexing its muscle as one of the greatest military forces the world has ever known, but on May 6, 1527 Rome failed to keep out a bloodthirsty army that spent the subsequent months murdering Romans and stripping the city of its wealth. Many of the invaders had a bigger target than mere looting: The Catholic Pope Clement VII. These early supporters of Martin Luther sought to imprison or ransom Clement VII, and standing between them and the Pope were a few hundred Swiss Guards, sworn to protect the Pope with their life. Their sacrifice during this Sack of Rome bought the precious minutes Clement VII needed to escape capture. His survival contributed to, in parts, motivating King Henry VIII from breaking from the Catholic Church, as well as promoting the Lutherans into their irrevocable break with the Church. And that's why the Last Stand of the Swiss Guard is a battle you might not know, but should.

You've heard of US military tragedies like Pearl Harbor and Custer's Last Stand, but arguably the worst defeat on a US army force is so unknown that it doesn't even have a name. Most call it St. Clair's defeat, named after the general who lost 1/3 of the US's standing army in a single morning. We call it Battle of the Wabash, named after the river where a smaller Native American force wiped out an American encampment on November 4, 1971.

Britain's introduction to "modern" warfare came a few years before World War I against an unlikely foe: farmers on horseback. Except these farmers geniusly employed smokeless powder, machine guns, and trenches. The farmers were called Boers, and 3,500 of them fended off 21,000 British troops at a small river crossing in South Africa called Colenso.