What are some factors that caused european nations and the united states to become involved in world war 1?

There are 5 main reasons why Europe got involved in the war.

Explanation:

There is a very simpla acronym to rememerb the reasons for Europe and their involvement in the war. The acronym goes as followed:

M.A.N.I.A

M = Militarism - military state or condition; reliance on military force in administering government; a military system.

A = Alliances - Alliances with fellow Europian countries involved in the war. Think fo it as if they are friends and somebody hit/threatened your friend, you would stand up for them right? That's similar with the situation of the alliances between European countries at the time.

N = Nationalism - Thinking your country is best, and the only one that matters.  A big ego, they wanted to protect and prove their nationalism to others and themselves.

I = Imperialism - a policy or ideology of extending the rule over peoples and other countries, for extending political and economic access, power and control.

A = Assasination  The assassination fo Franz Ferdinand is what started it all. Franz Ferdinand, the Archduke of Austria, was assassinated and the assasination was blamed on Serbia and hence the alliances interviened and started fghting with each other.

the answer is a. hope this