Second day of Yom Tov - where and why?

Kolel L'horaah Ma'asis Crown Heights - Shiur 25 on halachic topics - by Rabbi Shraga Dovid Homnick, Sgan Rosh Kolel, on the halachic questions about observing one or two days of Yom Tov that arose when Jews from Jerusalem fled to Ramla to avoid a barrage of persecution, and how the rule of 'one day of Yom Tov everywhere in Eretz Yisroel' is actually a recent development in halachic observance

https://www.youtube.com/watch?v=JCD67U6vfjU