During their United States mission, López wrote numerous dispatches to Aguinaldo and to the Central Committee at Hong-Kong urging a cessation of hostilities, pointing out that armed resistance could not secure independence, but would only confuse the issues and do injury to a good cause.

When the spate of hostilities between the Philippines and America erupted, the delegation left the US, but López soon returned to Boston, Massachusetts in 1900 to be a guest of Fiske Warren, an officer of the New England Anti-Imperialist League.

"In placing this statement before the people of America, I beg to assure them that whatever its demerits may be, it is the outcome of a sincere desire for peace and for an honorable settlement of the differences and difficulties of the Philippine question."

His moderate demeanor enabled him to establish close ties with Americans in Massachusetts, that soon he became an influential voice in the Anti-Imperialist League's shift from a nearly exclusive focus on the effects of imperialism on the United States to one, which included a component of solidarity with the Filipino people.

[1] His sister, Clemencia López, arrived in the U.S. in 1902 to secure the services of the famed jurist and future Supreme Court justice, Louis Brandeis in order to aid her brother's fight against deportation to Guam.