Coalition- An alliance for combined action, a temporary alliance of political parties forming a government or (a) state(s).
I assume your talking about the HUNS... When the empire split in two the east had more gold and more resources and the dying west had to suffer all the barbarian attacks like the huns... The East quite simply was more prepared and had more walls and guards to defend their border also the Eastern Empire had the river danube north of them which helped deflect the Hunnic invasions and other barbarian invasion more west...
Climate change that caused a severe drought.It is also theorized that the Hittite's cities were destroyed by earthquakes.
By approval, I think you mean by the delegates from each state had approved it. The problem was that the states themselves had to approve it. That seemed like a cumbersome process, but you have to remember that democracy works on the will of the people and each state had to ratify it keeping in mind that there were still problems: it was not a slam dunk.
D? I think i remember learning this. Sorry if its wrong!