Fascinating discussion by the Rebbe as to why Rashi comments on the reason for increasing simcha in Adar is because of the miracles of Purim and PESACH?!!

What is the nature of absolute simcha? - The Rebbe and Reb Velvel Brisker

What exactly must we do to increase our simcha in Adar? - the Munkatcher Rov in Nimukei Orach Chaim