I think a series of crippling natural disasters is the answer.
The one that is the msot effective to include is <span>US victory in the Spanish-American War in 1898.
</span><span>US victory in the Spanish-American War in 1898 basically help the majority of South American region to obtain their independence in the spanish.
This result of this war opened up a mutually beneficial relationship between us and southern american nations in term of trades, resources exchange, millitary alliance, etc.</span>
I would say b. the union
hope it helps :)
