After the Yom Kippur War in 5734, spanning the months of Nissan to Tammuz, terrorists infiltrated Eretz Yisroel and killed ר”ל many Yidden. (See footnote for more information on the four main attacks.)
At that time, an urgent call from the Rebbe directed at all Jews was published that included an excerpt from a sichah (linked below). In this sichah, the Rebbe pointed out the importance of each and every Jew becoming actively involved in the five mivtzoim (that had been established at that point).
The Rebbe explained how these mivtzoim each have the unique power to protect Jews from harm. The Rebbe concluded the sichah by saying that a mitzvah done in one location protects not only the one who does it, but also all Jews wherever they are, even those who have not yet fulfilled the mitzvos!
See the sicha here
The four main attacks in 5734:
The Kiryat Shmona massacre occurred on 19 Nissan, 5734. Three terrorists of the Popular Front for the Liberation of Palestine – General Command crossed the border from Lebanon to Eretz Yisroel and attacked Yidden in Kiryat Shmona. The terrorists killed 18 people, including 8 children, and wounded 16 others.
The Ma’alot massacre was a Palestinian terrorist attack that occurred in Iyar 1974. The attack involved taking 115 Yidden as hostages for over two days. The terrorists killed 25 hostages, including 22 children, and injured another 68.
On June 13, 1974, four Palestinian terrorists crossed the Lebanon-Israel border and attacked the kibbutz of Shamir in northern Israel. The terrorists killed three women before being killed themselves.
The 1974 Nahariya attack was a raid by three Palestinian terrorists, belonging to the Fatah terrorist organization, which took place during the night of 24–25 June, 1974. The Palestinian terrorist squad infiltrated the coastal city of Nahariya in Israel by sea from Lebanon. Three civilians and one Israeli soldier were killed during the event. The attack was the first time in which terrorists infiltrated into Israel from Lebanon by sea.