Why did the U.S. military invade Grenada back then

Reasons: oil transportation lines are threatened, subvert the current regime, and foster pro-US forces.

Grenada is a small island country in the Caribbean Sea, with an area of only 344 square kilometers and a population of 110,000, but it is located in the southern part of the Eastern Caribbean Sea, and is strategically important as it is a shipping lane from the Caribbean Sea to the two oceans. It was once a French and British colony, declared independence in 1974 and became a self-governing Commonwealth territory.

In 1979, Prime Minister Bishop came to power and pursued a pro-Soviet and Cuban policy. The U.S. believed that the pro-Soviet and Cuban Grenada posed a threat to the U.S. oil transportation lines, and thus had plans and preparations to subvert the current regime and foster pro-American forces.

On October 13, 1983, the political situation in the country began to be in turmoil.

On the 19th, former Prime Minister Bishop was executed, and the more pro-Cuban "radical left" took over the reins of power, setting up a Revolutionary Council headed by Army Commander Austin. Faced with this political change, the Organization of Eastern Caribbean States (OECS) met on Oct. 21 and demanded U.S. action.

On the 22nd, U.S. Vice President George W. Bush convened a meeting of the National Security Council and made a preliminary decision to send troops. The following day, President Reagan, who was on vacation, returned to Washington and reconvened the National Security Council.

At 6:00 p.m. on the evening of the 24th, Reagan signed an order to invade Grenada, code-named "Fury".

The invasion took place from October 25 to November 2, 1983, when the U.S. **** committed ground troops. The U.S.**** committed 7,200 ground troops (including 1,200 Marines, 700 Rangers, 5,000 Airborne Division troops, and 300 troops from seven Caribbean nations); 10,000 shipboard personnel, 15 ships, and more than 110 carrier aircraft. With a total of just over 1,000 Georgian troops*** and another 700 Cuban advisors and construction workers stationed on the island, the main battle on the island actually lasted four days, with all the fighting ending on November 2nd. After taking control of the situation on the island, the United States forces installed Governor Scoon, who had been appointed by the Queen of England, to re-establish a provisional government. After the main fighting on the island was over, the invasion force began withdrawing on October 28, and once the situation had stabilized, the rest of the force withdrew from the island. During the fighting, U.S. forces suffered 18 deaths and 19 injuries, while 7 helicopters were shot down and 11 wounded. In Cuba, 69 were killed and 642 were captured.

The U.S. surprise attack on Grenada is a typical war of aggression under modern conditions in open combat and a brutal intervention in a sovereign country. It is another larger-scale military action taken by the United States in Latin America following the armed intervention in 1965 in the Dominican **** and the country, but it is still only an island operation of limited scale, and according to the United States military doctrine, it is still a low-intensity war.