In the early 450s a string of deaths changed the political dynamic of Roman world. Between 450 and 455 Galla Placidia, Aelia Pulcheria, Atilla the Hun, Flavius Aetius and Valentinian III would all die- leaving the stage wide open for the next generation of leaders. 

Also, an announcment. 

In 451 Atilla the Hun invaded the West. He was repelled by a coalition of forces lead by the General Aetius. 

After placating Atilla with yet another indemnity, Theodosius II fell from his horse and died in 450, leaving the Eastern throne vacant.