Why was the revolution such a long and deadly conflict? ( P. S. I don’t understand what I’m learning but I know it has something to do with Mexican immigration.)

THIS ISN'T MINE (It's boardd620) but I like it sohere

Explanation:

The First World War 1914-1918 unfolded in two main theaters of operations - in Western and Eastern Europe, as well as in the Balkans and Northern Italy, in colonies - in Africa, China, Oceania. In 1914, all the participants in the war were going to win through a decisive offensive, and no one expected that the war would become protracted.

Entente countries were able to coordinate actions on two fronts - the Russian offensive in East Prussia coincided with the most difficult moment of battles for France, in fact, breaking the German blitzkrieg. Germany was forced to fight on two fronts at the same time, and also to carry out the transfer of troops from front to front, not being able to concentrate forces against one enemy.

Very soon after the outbreak of the war, it became clear that the clash would become protracted. The uncoordinated actions of the Entente countries, which possessed superiority, allowed Germany, the main military force of the Triple Alliance, to wage war on an equal footing. For the first time in this war, hostilities have become truly massive. For the first time, tanks, fighter aircraft, dreadnought ships, and chemical weapons were used.

i believe the correct answer is b.