What what I understand about it (being retired military). It's origins go back to Jimmy Carter, who first put the bug in the ear of the pentagon and top military brass. But we still kept using the famed M1911-A1 duringthe time Carter & Reagan werePresidents.

There were talks/demands of complying with NATO regulations and going to the 9mm, while we were expanding bases and acquiring new bases in Italy (home to Beretta). So that's how we came to use the Beretta M9 (Beretta 92) 9mm. Thisfinally come about when George Bush (Sr.)was President.