Achashverosh was a great king and ruling a huge kingdom. He threw a huge party to show 
that he is in control of all of the provinces and it showed that he is very wealthy, they drank out of gold goblets to show how wealthy the king was. His party was 180 days which was long enough to show off his leadership, his wealth and all his power that he had. At the end of his 180 days the last 7 days, Achashverosh threw another party where he invited everybody from all the provinces. 
Vashti, also threw a party for all the women. Achverosh wanted to bring vashti to the party to show off her beauty, but vashti  refused to go to the party and achveosh becomes furious. 
Achverosh had no power. It seems like he is the greatest most powerful king who ruled over 127 provinces but we see that he really isn't and he asks all of his advisors to do everything for him.