What is a technical word for an event causing conflict to escalate to war?

The word I am searching for is used in the field of International Relations. It is used to describe a specific event that causes an ongoing passive conflict to escalate into active conflict. It is similar to, but is not the word 'catalyst'.

The term indicated an event triggering a direct change from non-violent to violent action.

For example: The use of beef grease (tallow) in cartridges as the spark to the Indian Rebellion of 1857.

Example sentences:

The use of tallow in rifle cartridges [term] the Indian Rebellion of 1857.

In the case of Sri Lanka the two peoples had lived together under British rule but following their departure the desire by some Sinhalese to assert their culture as dominate over another was brought into the public sphere of politics by the Sri Lanka Freedom Party and became a [term] for violence to begin.

precipitant

Oxford English Dictionary

A cause of a particular action or event.

‘the immediate precipitants of the conflict’

Perhaps you meant casus belli:

An act or event that provokes or is used to justify war.

American Heritage® Dictionary

Casus belli is a Latin expression meaning "an act or event that provokes or is used to justify war" (literally, "a case of war"). A casus belli involves direct offenses or threats against the nation declaring the war, whereas a casus foederis involves offenses or threats against its ally—usually one bound by a mutual defense pact. Either may be considered an act of war.

https://en.wikipedia.org/wiki/Casus_belli

I suggest Flashpoint.

While the term doesn't seem to have the event-focus that you're looking for (or the starting letter), the connotations fit. It's a brewing passive conflict with the possibility of escalating to active war.

In the case of Sri Lanka the two peoples had lived together under British rule but following their departure the desire by some Sinhalese to assert their culture as dominate over another was brought into the public sphere of politics by the Sri Lanka Freedom Party and became a flashpoint for violence to begin.