Within three years of one another

" Then, as if to herald the coming century of colonization and conflict in the northern continent, three European powers planted three primitive outposts in three distant corners of the continent within three years of one another: the Spanish at Santa Fe in 1610, the French at Quebec in 1608, and, most consequentially for the future United States, the English at Jamestown, Virginia, in 1607." From The American Pageant ( AP U.S. History textbook)

What does "within three years of one another" mean here?