State-to-state negotiations that erupted into violence

In My Humble Opinion
1

As we know, diplomatic meetings are governed by elaborate protocol. We take it for granted that negotiators will stay calm and maintain decorum no matter how angry they might be at each other, and no matter what kind of bloodshed might be going on back home.

In recent history (say, the last 200 years), have there been any state-to-state negotiations that erupted into violence there in the room?

(The only instance I can think of is during the 1956 Hungarian Revolution, when – in the middle of talks – the head of the Soviet KGB arrested Hungary’s new minister of defense.)

2

The Toledo War. Surprisingly it was wanted once.

ETA: Nvrmnd. Badly misread the OP.

3

ISTR that Milovan Djilas was present at some meeting with Stalin in Moscow, while he was still a loyal follower of Tito and the Jugoslav Communists were still (just about) on speaking terms with Stalin, and something that was said to Stalin before the Jugoslavs left that led to Beria rough-housing one or other of them in the corridor outside.

And there’s Hitler’s treatment of the elderly president of the rump of Czechoslovakia before the complete Nazi annexation.

4

Inside the OP’s 200 year limit by two, in 1827 the Dey of Algiers struck the French envoy with jus fly whisk, which begat an invasion and 130 years of colonial war

Going a bit beyond 200 years, there’s this image of a breakdown in talks between Prussia and Austria

5

Negotiations between the US government and the Modoc nation in Northern California ended in the murders of Army Gen. Canby and peace commissioner Rev. Thomas in 1873.