Matchmaking in RTW was through Gamespy, I believe it was the same for M2TW. You'd go online, you'd have your lobby, a list of games and the details about them. If it was not identical to yours (modded), it would be red instead of yellow/gold.

ETW brought steam. That brought region games. I cannot play with anyone outside of Australia and a few surrounding countries, unless I can join off a steam friend.

What it meant for me is that I'd be lucky to have more than 5 people online in my area. Once you were in game, you could chat, but...it was dead.