Formed between Nasser's Egypt and Syria, it fell apart in the 60s (i think) due to Egyptian dominance, however Iraq was ready to join (hence the three stars formerly on its flag). What if a strong federal government with a more equal situation for the member states.
Could the UAR lasted for longer, would Saddam have been thrown off by a larger Baathist state or would he have risen to total power? A far more decisive Iraq-Iran War? Israel in a weaker position? Future member states (Libya attempted a similar thing with Tunisia, while by that time Egypt was quite pro-western so snubbed the possibility)?