[MRM]

I cheated and Googled a bit to supplement my dim knowledge. My understanding is that US military ranks are an amalgamation of British and European ranks, and have been modified to fit American tastes and needs over the centuries. What it has meant to be a "General" has evolved over the years and the US has expanded the general ranks (so to speak) a few times, particularly relating to the Civil War and WWII.

The use of combined name ranks, like Sargent-Major and Lieutenant Colonel was common in history. What we now call "Major General" was originally called "Sargent-Major General" and what we call "Lieutenant General" was originally called "Lieutenant Colonel General". Over the years the names were shortened. The US originally only had 1 star and 2 star generals, so Major General was senior to Brigadier General. When they expanded the rank to three stars, Lieutenant (Colonel) General was the natural name for the rank, which evolved to be called Lieutenant General, even though majors are senior to lieutenants.