On the third year of his kingdom, King Ahashverosh threw a party (=mishte, a drinking party). Ahashverosh party lasted for 187 days. His empire was so big that he had to set different times to properly entertain all his guests. Each week Ahashverosh would honor guests from different regions of his Empire (me'am lo'ez). The last seven days were dedicated to the people of Shushan, those who live close to his palace.
Why did Ahashverosh throw such a party? Some speculate that it was done to celebrate his conquest of Egypt or his victory over the Babylonians, who tried to rebel against him. The Megila is very explicit about the inner psychological motives of Ahashverosh to throw the biggest party ever: behar-oto, (1:4) "to display the wealth of his royal glory and the magnificence of his greatness". In other words: to show off. Ahashverosh was not the first, for sure not the last, rich or powerful man who throws a lavish party to show-off his wealth. Usually this is done to compensate for one's low self-esteem, or other inferiority complexes. In the case of Ahashverosh it is ver clear that the man was terribly insecure, hesitant and doubtful (1:15, 7:7 and many others).
In any case, the Megila also shows the unlimited nature of ostentation. The text uses this term "lehar-ot", (to display, to show off) one more time in 1:11. On the very last day of the 187 days party, Ahashverosh "merry with wine" summoned up his wife. She had to be escorted to his presence naked, dressed only with her crown "to show the commoners and the officers her beauty".
The message is loud, clear and horrendous: Look at this rich but miserable man, who cannot control his urge to show-off. Once he was done exhibiting all his riches, he found one more thing to show-off: his trophy wife, Queen Vashty!
Ostentation is self destructive. And expectedly, the end of the party is tragic. Vashty was executed for refusing to follow the Royal order. And Ahashverosh, who invested so much in a party meant to boost his ego, ended up disgraced and humiliated by all (1:18).