Why did James Monroe and Robert Livingston act quickly to buy the Louisiana Territory? They felt that the purchase could stop a potential war between the US and France.
They knew that President Jefferson would disagree with the price and the amount of land.
They worried that President Jefferson did not have the authority to make the purchase.
They were afraid that Napoléon might change his mind and revoke the agreement.

 it is D, They were afraid that Napoléon might change his mind and revoke the agreement.

Explanation: the french was like yea and said he would sell all the land for 15 mill and they came only expecting just a little of the land so they wanted to act fast before he changed his mind

yes they have. but is this a true false question? if it is, the answer is true.

the monroe doctrine is the best known u.s. policy toward the western hemisphere. buried in a routine annual message delivered to congress by president james monroe in december 1823, the doctrine warns european nations that the united states would not tolerate further colonization or puppet monarchs.