Select these answers:
1. competitiveness brought on by imperialism
2. the rise in nationalism
3. the build-up of arms
5. the race for military supremacy
The military buildup became an arms race between the nations of Europe and increased tensions between the nations of Europe. Along with increasing expenditures on military forces and navies, there was pressure to form alliances with other nations to strengthen a nation's defenses in case there was a war.
There was also much competition between European countries for imperial dominance in other parts of the world. When war broke out between those European countries, it pulled their imperial and colonial holdings into the conflict too.
Nationalism also played a role, with nations feeling they should assert their supremacy over rival nations.