Are there historical examples of countries or kingdoms that did a complete 180 on their old allies - not counting vassals or similars changing one master for another?
We don't have an Ask Historians yet, so I think this is the best place to ask at the moment
Italy, both world wars if you count that
Italy, twice, on both world wars.
The Sino-Soviet split is similar. Neither was the other's "master," but relations deteriorated.
Though the split happened because the Soviets thought they should be master of all Communist countries and the Chinese had different ideas on the topic.
It's a lot more complicated and messy than that, and for what it's worth they nearly repaired relations before the USSR dissolved.
Yeah, pretty much standard in hostile regime changes. ROC to PRC, Russian Empire to USSR, Italy multiple times, happens literally all the time in third world countries where regimes are toppled by first world backed forces to install a government more friendly to said first world country (pretty much exactly what happened in the US tbh)
If we take "old allies" not so much as old friends but more as "previously allied with:" Japan was on the side of the allies in WW1 but was axis in round 2. Nazi-Germany invaded the USSR in spite of their peace pact. Napoleon and tsar Alexander of Russia were on somewhat friendly terms before Alex clandestinely rejoined the coalition against the French.
Yes, the Diplomatic Revolution for one.