8. The Spanish-American War: $9 billion
On the eighth place we have The Spanish-American War which had total costs of $9 billion.
It happened on the time when Spain was in control of Cuba, which was just off Florida.
The US had managed to secure great parts of land in the West and now they turned the attention to the Southeast.
It was only expected that Washington will demand that Spain turn over control from Cuba to the U.S.
And when Spain rejected the demand, the war began, and they fought for one year from 1898 to 1899.
This started American expansionist policy, as they took over Cuba, Puerto Rico, Guam and the Philippines.
