The Alshich says that the nation refers specifically to Benyamin, Mordechai’s ancestor.
According to the Talmud (Megillah 13b), the nation to which Haman aims his hatred is the rabbis – the elite leadership of the nation. M’nos HaLevi tells us that killing the rabbis would leave the Jews as sheep without a shepherd. The Jewish nation cannot survive without Torah leadership. The Yad HaMelech says Haman did not want to kill out the Jews, but only wanted to kill out the rabbis. His intent would be to enrage the Jews over the death of the rabbis, and blame Mordechai. They would then kill Mordechai, themselves. Haman believed that, this way, they would deserve to be wiped out by H-Shem. This idea of causing the Jews to deserve their own destruction is nothing new. Both Bilaam and Haman attempted just such a strategy in the incident of the daughters of Moav (Bamidbar 25:1-3) and Achashverosh’s party (Esther 1:1-10), respectively.
Why such hatred? Why did Haman so want to kill out the Jews? The Malbim and Akeidas Yitzchak posit that, since Mordechai refused to bow to him on religious grounds, Haman desired the death of that nation that followed those self-same tenets.
In his Vedibarta Bam on Megillas Esther, Rabbi Bogomilsky brings that Haman realized that all of the Yehudim were an “am Mordechai” – a nation of Mordechais. Even if Haman were to eliminate that Mordechai who won’t bow to him, there will be other “Mordechais” who will pop up to do the same.
Rabbi Yitzchak Blazer asks why, if Haman wanted everyone to bow to him, did he not simply decree that Mordechai have to do it. Seeing their leader doing so should inspire most people to ape that behavior. Rav Blazer answers that Jews are different. If we see our leader acting contrary to our beliefs, we feel disgusted by that leader, and want nothing to do with him.
According to the Ben Ish Chai, he wanted to kill the Jews due to his slave status. As his master, Mordechai could take possession over everything Haman owned. With Mordechai dead, a relative or other heir would become lord over Haman’s assets, leaving him virtually powerless. As long as there is a Jew alive, Haman could not have power. Power-hungry to his core, Haman needed to be rid of all possible heirs to Mordechai’s property, and this included all of the Jews.