Ever since 1526, the land that is now the Czech Republic had been under the rule of the Austrian Empire, but by the time World War One broke out in 1914, many Czechs wanted freedom and independence from Austrian rule. As such, many Czechs joined the armies of the Entente Powers fighting against Austria, including France, Italy, and, most importantly, Russia.
The Czech Legion serving under Russian command served bravely throughout the war, most notably in 1917 at the Battle of Zborov in Ukraine, where they inflicted a severe defeat on the Austrians and Germans. However, despite the valiant efforts of the Russian and Czech armies, the Bolshevik Revolution broke out in October of 1917, dividing the Russians between communist and anti-communist factions, and crippling their war effort against the Germans. The Czechs on the other hand, were determined to continue the fight, and decided to try and fight their way across Russia (a pretty tall order, what with Russia being the largest country on Earth and all) and then sail to France to fight on the Western Front. And so, in May, 1918, the Czechs fought off several German assaults in the Ukraine and started their epic quest across Russia.
Although the Russian Communists promised not to interfere with the Czechs' journey, tensions were on the rise between them and the Czechs as they headed towards Russia's Pacific port at Vladivostok, until, on May 14, the Russians attempted to arrest the Czechs at Chelyabinsk. The Czechs refused to surrender, leading to outright war between them and the Russian Communists. They continued to fight along the Siberian railway throughout the rest of May 1918, with the Czechs winning most of the battles despite being severely outnumbered (including one battle in which they allegedly managed to make off with most of the communists' gold), and by the end of the month, the Czechs had reached Vladivostok and overthrew the local communist government. The Soviets were so terrified of the Czechs that they executed the Tsar and his family so the Czechs couldn't rescue them. It's a shame that the Czechs didn't arrive in time to save them too, since if the Tsar's family had lived the movie Anastasia wouldn't have been made, which would be a net gain for humanity.
Throughout their journey through Russia the Czechs escorted a number of Russian refugees from the communists (mostly women and children) to safety in the Western countries.
Although the war had ended by the time the Czechs made it home in 1920, the Entente powers of Britain, France, America, and Italy were so impressed by the Czechs' bravery that they agreed to create an independent Czech nation, whose army was mostly made up of veterans of the Legion.
In conclusion, I think it's a shame that this, one of the coolest epics of World War One, has been largely forgotten, (except among Czechs and Slovaks of course) and all I have to say to the people who forgot about it is... Czech your privilege!...
...I'm sorry...