Lag B'Omer (the 30th [day] of the [counting of the] Omer)
c 1436 BCE- The battle against Ai in the days of Joshua.
c 120 CE- The plague among Rabbi Akiva's disciples ends. In the weeks between Pesach and Shavuot [Pentecost], a plague decimated 24,000 students of the great sage Rab' Akiva - a result, says the Talmud, of the fact that they "did not respect one another." The plague's cessation on Iyar 18 - the 33rd day of the Omer Count or "Lag Ba'Omer" - is one of the reasons that the day is celebrated each year. Also, On Lag Ba’omer Rab' Akiva gave Semicha to his five talmidim who did not die, and through whom Torah was disseminated, (among them Rab' Shimon Bar Yochai).
c 1573- Yahrtzeit of HaRav Moshe Isereles (the Rema), of Cracow, Poland. His most famous work was the glosses ("hagga'ot") on R. Yosef Caro's Shulchan Aruch (the Code of Jewish Law); these opinions are regarded as the definitive Halachic authority for Ashkenazic Jews.
1370- Hundreds of Jews were burned alive in Brussels, and the remainder were banished from the country.
April 27, 1690- The Jewish community of Ettingen, Germany, set this day aside as a day of thanksgiving for their escape from blood-libel charges.
May 27, 1948- The Churva synagogue located in the Jewish quarter of the Old City of Jerusalem, was captured and dynamited by the Arab Legion of Jordan during the battle for the Old City. The synagogue was built by the group of disciples of Rab' Eliyahu (the "Vilna Gaon") who immigrated from Lithuania in 1864. The synagogue was built on the ruins of the synagogue built by Rabbi Yehudah Chassid (Segal) and his disciples in 1700, which was destroyed by Arab mobs in 1721. It was therefore named the "Churvat Rabbi Yehudah HaChassid" -- the ruins of Rabbi Judah the Chassid, or simply "The Churva" -- The Ruin. It was rebuilt and reopened in 2011.
The Jewish community of the Old City surrendered to Jordan’s Arab Legion.
The Israel Defense Forces (IDF) was created on Lag BaOmer of 1948. The IDF comprises the Israeli army, air force and navy. It was formed to defend the existence, territorial integrity and sovereignty of the state of Israel and combat all forms of terrorism which threaten the daily lives of its inhabitants.