Franz Ferdinand was the prince of Hungary and an archduke of Austria- Este. When he was assassinated, his nation delared war on Serbia.
On christmas eve they called a truce and sung christmas carols. Some even said that the germans were singing joyously with the enemy.
The phrase, 'You Shall Not Pass', was most famously used by the French General Robert Nivelle during this battle.
A battle between the German and the British. Around 58,000 lives were lost, which is 1/3 of the troops.