Kim Kardashian is the U.N. in Kylie and Blac Chyna's Truce

Kylie Jenner and Blac Chyna's war came to an end when big sis Kim Kardashian stepped in to play peacemaker.

Sources close to Blac Chyna tell TMZ she got a call from Kim several weeks ago to hash out the drama over her and Rob Kardashian's engagement. Chyna obliged and went to Kim's pad for the sit-down.

We're told they both agreed there was no reason for family beef over Rob and Chyna getting hitched -- since the more important point was Rob being happy, and getting out of the house again.

The peace summit also covered Tyga -- y'know, the fact he's dating Kylie and is also Chyna's baby daddy. We're told Kim made it clear the time was right for the ladies to chat.

A few days later Kylie and Chyna talked on the phone, which led to Thursday's face-swapping Snapchat session -- and an agreement to squash all beef.