Genesis chapter 19 records the two angels, disguised as human men, visiting Sodom and Gomorrah. Lot met the angels in the city square and urged them to stay at his house. The angels agreed. The Bible then informs us, "Before they had gone to bed, all the men from every part of the city of Sodom — both young and old — surrounded the house. They called to Lot, 'Where are the men who came to you tonight? Bring them out to us so that we can have sex with them.'" The angels then proceed to blind all the men of Sodom and Gomorrah and urge Lot and his family to flee from the cities to escape the wrath that God was about to deliver. Lot and his family flee the city, and then "the LORD rained down burning sulfur on Sodom and Gomorrah — from the LORD out of the heavens. Thus he overthrew those cities and the entire plain, including all those living in the cities..."
In light of the passage, the most common response to the question "What was the sin of Sodom and Gomorrah?" is that it was homosexuality. That is how the term "sodomy" came to be used to refer to anal sex between two men, whether consensual or forced. Clearly, homosexuality was part of why God destroyed the two cities. The men of Sodom and Gomorrah wanted to perform homosexual gang rape on the two angels (who were disguised as men). At the same time, it is not biblical to say that homosexuality was the exclusive reason why God destroyed Sodom and Gomorrah. The cities of Sodom and Gomorrah were definitely not exclusive in terms of the sins in which they indulged.
While being a homosexual was not the ONLY reason the cities were destroyed, you can bet it was not in-hospitality.
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