The first and to date only Interplanetary war between "Major Powers". While losses were minimal, the public outcry to them caused the end of the war before Earth could even send their troops over.
From the declaration of independence by the martian colonists of Utopia Colony shortly after the closing of the martian transfer window, to the day later response formally declaring war against the colony, for fear of this spreading, this war was incredibly brief. The combat was entirely revolved around a single battle when UN security forces stationed a few hundred km away arrived by rover and were refused entry. They eventually fired upon the settlement, causing a hull breach and 7 total deaths. Video of the event made its way back to earth, and the public, especially those from countries that had won their independence, called out for the cessation of hostilities. This eventually happened a few months later, leading to the founding of the PDRM.