Diplomacy is a game with the following properties:

1. It's not possible to eliminate someone else without another player's help, particularly early in the game

2. There can be only one winner

So "temporary alliances" which are eventually broken are built into the structure of the game; and unlike the "Surviror"-style game here, there's no "payback" round at the end, where the people you've betrayed get to vote against you. I'm not up on the culture of the game, but I'd be surprised if explicit in-game lying isn't considered fair play (e.g., you're not supposed to hold a grudge in real life against someone who lied to you in the game).

I played it once and really didn't enjoy it. With practice I might be able to bifurcate my sense of morals -- I do actually enjoy playing games like Mafia, Resistance, Avalon, etc. But I didn't feel like it would be worth my effort.

Diplomacy is a multi-player board game. Successful play tends to involve well timed betrayals.