As anyone who ever reads this blog (Hi, honey! Hi, kids!) knows, I think about AD&D 1e far too much. And oddly. I really like to consider how much little changes can make in the game. Today's though experiment:
What if Elves were not a playable race?
And by this I mean; elves are "monsters" (only seen as random encounters in groups as described in the monster manual) that do not mix with humans. They are, effectively, tall, less magical, Brownies. If, if, half-elves exist they are also 'monsters' like Cambions or something. How would this impact your game world?
One- Magic-users are human. Without elves and half-elves only Humans can be magic-users.
Two- The most common multi-class combinations don't exist. Fighter/magic-users? Magic-user/thieves? Fighter/magic-user/thieves? They don't exist. You will never have a fighter that can cast Fireball or a thief that can cast Knock.
Three- Gnomes are much more important as possible party members. They can be illusionists, fighter/illusionists, and illusionist/thieves, replacing the typical most common multi-class combos.
Four- Half-orcs are also much more important as the only real Cleric multi-class option and, RAW, the only truly viable non-human cleric at all.
There are other, more minor, effects - but that is plenty. The changes of just dropping one race are huge and far reaching, mainly by making magic-users 1) always human and 2) never multi-classed.