21. During the World War I most battles lasted a long time as it can be expected from the war that was mostly trench warfare. The two examples of then modern military technology were the use of poison gas and the use of submarine. The submarine was a novelty in the war though it was most effective in terms of economic warfare as they could attack the supply ships. The sinking of the US trade ship by a German submarine was on of the reasons the US entered the WWI. The poison gas was one of the most terrifying weapons that was used during the WWI and it led to the use of masks on the battlefield.
2. France and Germany controlled much of the known world at the time and basically there was no more land for the taking. Germany entered late in the colonization race and thus had bad relations with the two, especially France as there were several diplomatic incidents that almost resulted in war.
