The schools of Shammai and Hillel for the very first time disagreed regarding a case of Jewish law. This occurred around the turn of the 1st century. In the ensuing generations, the schools argued regarding many different laws, until the law was established according to the teachings of the "House of Hillel" -- with the exception of a few instances. According to tradition, following the arrival of the Moshiach the law will follow the rulings of the House of Shammai.

All throughout, the members of the two schools maintained friendly relations with each other.

Link: Houses of Shammai & Hillel

After a 12-day sea voyage, the previous Lubavitcher Rebbe, Rabbi Yosef Yitzchak Schneersohn (1880-1950), disembarked at the New York harbor on the 9th of Adar II of 1940, following his miraculous rescue from Nazi-occupied Warsaw.

Link: Vintage film clip of the Rebbe's arrival in NY, March 19, 1940; more about Rabbi Yosef Yitzchak of Lubavitch.

This being the Shabbat before Purim, on which we celebrate the foiling of Haman the Amalekite's plot to destroy the Jewish people, the weekly Parshah is supplemented with the Zachor reading (Deuteronomy 25:17-19) in which we are commanded to remember the evil of Amalek and to eradicate it from the face of the earth.

"Parshat Zachor" is the second of four special readings added during or immediately before the month of Adar (the other three being "Shekalim", "Parah" and "Hachodesh")

Links:
The Zachor Reading with commentary
More on Amalek