In his first State of the Union Address, President Theodore Roosevelt explained the need for national antitrust legislation:

The large corporations, commonly called trusts, though organized in one State, always do business in many States, often doing very little business in the State where they are incorporated. There is utter lack of uniformity in the State laws about them; and as no State has any exclusive interest in or power over their acts, it has in practice proved impossible to get adequate regulation through State action. Therefore, in the interest of the whole people, the Nation should, without interfering with the power of the States in the matter itself, also assume power of supervision and regulation over all corporations doing an interstate business.

Source:

James D. Richardson, ed., A Compilation of the Messages and Papers of the Presidents, 20 volumes (New York...