Simplify the following text for a Grade 9 native English-speaking person.
Original: At the Fourth International Conference of American States ( Buenos Aires , 1910 ) , the name of the organization was changed to the `` Union of American Republics '' and the Bureau became the `` Pan American Union '' .
Simplified: In 1910 , these countries held the Fourth International Conference of American States at Buenos Aires . They changed the name of the International Union of American Republics to the Union of American Republics .