The answer is the revolution that declared Mexico as an independent country. Both countries knew that they can benefit from it in terms of free trade and migration which promotes economic development. Spain was not happy of such negotiation. They believe that the trade will jeopardize the safety of Mexico. Mexico paid no heed and continued with the agreement with the United States.
The correct answer is revolution.
Revolution spurred American trade with northern Mexico.
Both Mexico and America they were sharing land border and maritime which was found in the North America.
Both countries had economic and diplomatic ties on the regime of Diaz as the president.
It is in this period of Diaz as the president where Mexico were able to open foreign investment where entrepreneurs from US invested in mining, agricultural enterprise and ranching.
In the revolution of Mexico U.S had a role which was important.
