Nationalism: Each country wanted to prove that they were better than the rest with dominance and power throughout Europe and Asia.
Imperialism: In Africa, there were several territories under claim between different European countries because of the rights to exploit areas with a lot of raw materials.
Alliances: Neighbors countries had mutual defense agreements that provide an alliance if any of the countries were attacked by a foreign nation, the other country would be bound to intervene and help. There were alliances between Russia and Serbia; Germany and Austria-Hungary; Britain-France-Belgium.
Militarism: The growing arms race in Europe along with the nationalism feeling across the continent, made that each country wanted to increase its own army to show the power and eventually led to the war.
The south had a smaller army, and less technological advances than the north. But they had better commanders and they knew the land better than the north.
The North had a smaller war spirit and they didn't know the land. But they had bigger armies with the support of many slaves, they also had better technological advances than the south.
A tax protest by western Massachusetts farmers in 1786 and 1787 showed the central government couldn’t put down an internal rebellion. It had to rely on a state militia sponsored by private Boston business people.
