Around 1900, european nations built up their military forces, formed alliances, and expanded their colonial holdings in their efforts to

1 force their enemies to start wars.
2 maintain a balance of power.
3 put a conscription system in place.
4 end the spirit of militarism.

The correct answer is maintain a balance of power. Basically, countries started investing in defense because they saw how some other countries were behaving and how much anger there was. They started investing in their defense and it led to a mass accumulation of weaponry where the militaries and the supplies nearly doubled in the time period between 1890 and 1930.

The answer to that question is a