The 20th century was very special when it came to war and war fighting. While the industrial revolution saw ships turned into floating gun platforms, and the Crimean War was the last battle of the sail, the 20th century was primed as an apex of technologically driven warfare. In the 1880s, Dr. Gatling thought his invention would stop all wars because no one would ever want to face his gun on the battlefield. So too it was with many of the weapons innovations of the 20th century.
While the goal of military engineers of the 19th century was to simply mass produce death, their 20th century counterparts reached the zenith of mass murder with shocking alacrity, and the new design objectives military engineers were given were mostly around accuracy, and methodology. The 20th century saw the creation of tactical nuclear weapons as well as the invention (although not production, thank God) of the so-called Flying Crowbar, a nuclear weapon capable of destroying the whole world with one launch.
Enter into this explosion of innovation the many nations eager to make war and you have a world full of wars unlike any fought before or since. The question remains: How much do you know about the military invasions of the 20th century?