With expanding international interests, he supported Cuban independence, helped found the League of Peace in 1908 and served as its president.

McDowell was a founding trustee in 1881 of the American Institute of Christian Philosophy, together with Cornelius Vanderbilt II and several learned ministers.

His interest in international affairs led him to become a leader in the universal peace movement of the late nineteenth and early twentieth centuries.

[4] The industrialist Andrew Carnegie was also among the founders,[5] and President Theodore Roosevelt supported the League of Peace in a 1910 speech.

[6] On October 5, 1912, McDowell as president of the League of Peace, delivered a tribute in London to the poet Alfred Lord Tennyson, who dreamed of "the Parliament of man, the Federation of world.

"[7] In 1913 McDowell attended, as a representative of the State of New York, the dedication of the Peace Palace, the site of the International Court of Justice, in The Hague.

McDowell wanted the heritage organization to become a mass movement with broad and generous membership requirements, to recognize descendants of patriots who had a variety of roles in supporting the Revolution - not necessarily in military service.

At this convention, he founded the Sons of the American Revolution on April 30, 1889, to represent his vision of a broader based society.

He initiated the Columbian Liberty Bell project, which sent a replica of the Liberty Bell on tour throughout the U.S.[2] McDowell was a companion of the District of Columbia Commandery of the Military Order of the Loyal Legion of the United States by right of inheritance from his father, Brevet Colonel Augustus William McDowell, who had served as a surgeon in the Union Army.

[2] The DAR was founded by women descendants of Revolutionary-era patriots; they were interested in historic preservation and irritated at having been excluded from the men's organizations.

Her actions were also prompted by what she said were McDowell's ambition to exploit the SAR and DAR as organizations on which to build a presidential campaign.