In the case of Israel's invasion of Lebanon in 1982, act of response to terrorist attacks ________ was used this justification for the invasion.

The question refers to Israel's invasion of Lebanon in 1982. This event, known as Operation Peace for Galilee, was launched by Israel with the stated goal of creating a 40-kilometer buffer zone in southern Lebanon to protect its northern settlements from attacks by the Palestine Liberation Organization (PLO).

Israel justified the invasion as an act of self-defense or retaliation against ongoing terrorist attacks and shelling from the PLO, which was based in southern Lebanon. A key immediate trigger was the attempted assassination of Israel's ambassador to the UK, Shlomo Argov, by the Abu Nidal Organization, which Israel attributed to the PLO.

The first blank asks for the "act of ______", referring to the nature of the invasion's justification. The second blank asks for the "terrorist attacks ______", referring to the group responsible for these attacks.

The completed sentence is:
In the case of Israel's invasion of Lebanon in 1982, act of self-defense in response to terrorist attacks by the Palestine Liberation Organization (PLO) was used this justification for the invasion.

The first blank is: self-defense
The second blank is: Palestine Liberation Organization (PLO)