Tensions between the two would eventually boil over in 2512, when a dispute over metal exports led to a blockade of Gauusian trade routes by Terra. Seen as an existential threat, Gauus would declare full independence, severing all of its ties to the alliance. Military engagements would start occuring not long after, with Terran fleets attempting to enforce the blockade. Gauus' military infrastructure, however, had significantly advanced, with early skirmishes usually resulting in UNIA fleets retreating from skirmishes. These conflicts would remain primarily naval for the first couple of years, with both sides attempting to control key trade routes and resource deposits. Gauus' extensive knowledge of the outer Hydrus System - particularly of it's resource-rich deposits - would give them an early advantage.

Things would extend beyond simple skirmishes by 2515, with the conflict escalating into full-scale interplanetary war. By this point, the UNIA had called on the other planets to support the campaign against Gauus, as they feared for a total collapse of the alliance. Acwai pledged it's fleets to the war, with Kontrol's fleets (Myrl) following shortly after.

In response, Gauus started targeting UNIA supply chains and communication lines from the two planets, hoping to cripple their ability to engage in the war. One of the most infamous operations during this period would be the Eventidal Siege, which saw Gauusian forces blocking the water-world from the rest of the system. The siege inflicted major damages to Acwai's economy, but was eventually lifted by combined UNIA forces in 2517.