Hello there 753B.C.E.-509B.C.E. roman monarchy 509B.C.E.-27B.C.E. roman republic 395C.E.-476C.E.western roman empire 395 C.E.-1453C.E. byzantine empire(eastern) 27b.c.e.-395c.e. is unidentified means Byzantine is the longest ~hope i help~
It impacted politics in the mid-19th century because of the large inflows of immigrants after 1845 from cultures that were different from the existing American culture.