What explains the large number of US Security Council vetoes between 1970-1991?

Apparently I was mislead by the formal version of the Negroponte doctrine. It had less formal predecessors. The 1993 article from which I'm quoting the passage below does seem to have a certain political bias, but on the bare stats, it's probably correct:

Two years later, however, on Sept. 10, 1972, the United States employed its veto for the second time—to shield Israel.' That veto, as it turned out, signalled the start of a cynical policy to use the U.S. veto repeatedly to shield Israel from international criticism, censure and sanctions.

Before this practice stopped 18 years later, Washington used its veto 29 times to shield Israel from critical draft resolutions. This constituted nearly half of the total of 69 U.S. vetoes cast since the founding of the U.N. The Soviet Union cast 115 vetoes during the same period.

The initial 1972 veto to protect Israel was cast by George Bush in his capacity as U.S. ambassador to the world body. Ironically, it was Bush as president who stopped the use of the veto to shield Israel 18 years later. The last such veto was cast on May 31, 1990, killing a resolution approved by all 14 other council members to send a U.N. mission to study Israeli abuses of Palestinians in the occupied territories.

The rationale for casting the first veto to protect Israel was explained by Bush at the time as a new policy to combat terrorists. The draft resolution had condemned Israel's heavy air attacks against Lebanon and Syria, starting Sept. 6, the day after 11 Israeli athletes were killed at the 1972 Munich Olympic Games in an abortive Palestinian attempt to seize them as hostages to trade for Palestinians in Israeli prisons.3 Between 200 and 500 Lebanese, Syrians and Palestinians, mostly civilians, were killed in the Israeli raids.

Nonetheless, Bush complained that the resolution had failed to condemn terrorist attacks against Israel, adding: "We are implementing a new policy that is much broader than that of the question of Israel and the Jews. What is involved is the problem of terrorism, a matter that goes right to the heart of our civilized life."

Unfortunately, this "policy" proved to be only a rationale for protecting Israel from censure for violating a broad range of international laws. This became very clear when the next U.S. veto was cast a year later, on July 26, 1973. It had nothing to do with terrorism. The draft resolution affirmed the rights of the Palestinians and established provisions for Israeli withdrawal from occupied territories as embodied in previous General Assembly resolutions. Nonetheless, Washington killed this international effort to end Israel's occupation of Palestinian lands.

The Carter administration cast only one veto. But it had nothing to do with terrorism. It came on April 30, 1980, killing a draft that endorsed self-determination for the Palestinian people.

The all-time abuser of the veto was the administration of Ronald Reagan, the most pro-Israel presidency in U.S. history, with the most pro-Israel secretary of state, George Shultz, since Kissinger. The Reagan team cynically invoked the veto 18 times to protect Israel. A record six of these vetoes were cast in 1982 alone. Nine of the Reagan vetoes resulted directly from Security Council attempts to condemn Israel's 1982 invasion of Lebanon, and Israel's refusal to surrender the territory in southern Lebanon which it still occupies today. The other nine vetoes shielded Israel from council criticism for such illicit acts as the Feb. 4, 1986, skyjacking of a Libyan plane.

Still it would be interesting to know whether any other themes dominated the rest of the 40 (= 69-29) US vetoes, not related to Israel, in this time 1970-1993 frame.