Me will give you brainliest for correct answer there were four main causes of world war i. give three and explain how each led to the war in the space below.

1. Materialism, Britain already had an army. Which led to Germany being jealous, making France and Germany compete to see who has much more armies.

2. Alliances, has been said that Europe has always been making alliances. Of course alliances would be said to make "peace". It was disastrous because if there were to be a fight between to countries, other countries who have an alliance with them had to join too. It was the countries Austria and Serbia which led to WW1.

3. Last would be Nationalism. Of course one had pride on their homeland. The countries had the idea that their country was mightier than the others. Nationalism is what led Europe nations to build the biggest army and navy.

Hope this helps!

c, they united with once

the answer is definitley b!