ICR: Ioannis Casimir Rex and a play on words: Initium Calamitatis Regni (beginning of the countries mishap)

What does ICR mean? The above is one of ICR meanings. It may have other definitions. Please refer to the end of this passage.

Definition in English: Ioannis Casimir Rex and a play on words: Initium Calamitatis Regni (beginning of the countries mishap)