There are many diplomatic incidents that had a non-zero chance of resulting in war (Even if in a small scale), some of whom I can name are:
- Nootka Crisis - Envolves an indigenous tribe, the Spanish Empire, Great Britain and the US. Would probably be a minor war, with a status quo result.
- Fashoda Incident - Could escalate into an African conflict between France and the UK
- Falklands Crisis of 1770 - One of the most interesting of all, had it resulted in a war, it would've pitted France and Spain against the British and could've butterflied away (or at least delay) the American Revolution
- Oregon boundary dispute - If one of the sides had been unwilling to compromise, we could've seen a war between Britain and the US, possibly happening at the same time as the Mexican-American War