The five-arrow symbol represents the founding of the Iroquois League, or the Haudenosaunee Confederation, as it's also known, by the Peacemaker in 1142. As the symbol would suggest, the founding of the Confederation involved the coming together of five nations, each with its own distinct culture, language, and hunting grounds. According to tribal legend, the Peacemaker united the five nations into a single Confederacy because he believed they'd be much stronger together than if they remained separate. "United we stand, divided we fall," as the saying goes.
Haudenosaunee means "People of the Longhouse" and is often used in preference to the term "Iroquois," which is thought by many to have derogatory, colonialist connotations. Whichever term is used, the Confederacy originally consisted of the Mohawk, Oneida, Onondaga, Cayuga, and Seneca nations—one nation for each arrow of the Confederacy's symbol.