Why did the united states sign a treaty with spain?

Pinckney's Treaty (1795) established a positive relationship between the United States and Spain. The treaty defined the boundaries of the United States with the Spanish colonies and guaranteed the United States navigation rights on the Mississippi River.

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The United States purchased the Spanish-colonized-countries such as Philippine Archipelago, Cuba, Puerto Rico, Guam and some parts in North America under the Treaty of Paris on December 10, 1898 and came into full effect on April 9, 1899 after the ratification. This became the indicator that the Spanish-American War has ended. The Spain sold the Philppine archipelago for $20,000,000 after colonizing it for 333 years. Simply, through the Treaty of Paris, the United States got all the remaining countries colonized by the Spanish empire.    

The answer b is correct this all occurred during the red scare