The Coalition-Judean War was fought for six months in 2703 between the Coalition of Western Republics and the Democratic Republic of Judea. It was considered the bloodiest conflict in the Milky Way until the Galactic War that saw the the military of Judea clinging on for dear life on Tel Aviv. Only Kassel Confederate intervention and fear of greater conflict prevented the full destruction of the Judean state. Even today, the war prevents anything friendlier than animosity in diplomatic relations between the two states.
The cause of the war is unknown to any state aside from the Coalition itself. Even within the Coalition the cause is officially a "terror attack against major Coalition installations in orbit around Sol." What is known by most states is that Sol wasn't touched by either party before or during the war. Even Judea itself is in the dark to why exactly the Coalition attacked. According to Judean intelligence, a Coalition superluminal node, FF-14, experienced major technological issues, ranging from power loss to wormhole destabilization, because of a communications package from a Judean diplomat caused an overload in the system. Why such an important superluminal node would be overloaded by such a small package is unknown, but it is generally accepted that an extremely large message between the Coalition and an unknown target was also being managed by the FF-14, which was unable to process the data after the Judean message. The nature of the message and the target is unknown, but it is rumored to have something to do with a Coalition plan to end their isolationism and bring the systems of the Inner Sphere into their fold. The centerpiece of many of these conspiracy theories is the system designated BN-N100, since the Coalition government refuses to confirm or deny any theories about its identity or the Coalition's plans for it.
Regardless of the cause, the breakdown of the FF-14 enraged the Coalition's government, which immediately declared war on Judea. As soon as the node was repaired it was used to bombard the Judean communications network with anti-Judean propaganda, almost causing a collapse of all Judean electronic communications. Military action soon followed. The Coalition mobilized from various naval bases in the area and the systems of Kanto and Ocarina were bombarded and later occupied by the Coalition military. The Judean response was controlled retreat; knowing that a counterattack would simply enrage the Coalition more, Judean military personnel were ordered not to engage Coalition forces unless they themselves were attacked. A minor border skirmish between the Coalition and Kassel also sprung up, due to Kassel wishing to protect the Judean state as it was moving away from the Communist International. Much like Judea before them, the Coalition never actively attacked Kassel, because of its important role in the Inner Sphere and its membership in the Springfield Pact. Kassel declared a ceasefire after a day of fighting. However, the border war scared the Coalition that continued aggression against Judea would mean it would lose its allies in the Belt. In the meanwhile, Sorrento, holding expansionist views against Kassel, supported the Coalition war effort and wished to join the war against Judea, but could not because most of its navy was being retrofitted.
In six days, the remnants of the Judean military were holding out against the overwhelming Coalition forces in Tel Aviv. Later in the day a Coalition diplomat was sent to Judean authorities to declare a ceasefire between the two states, as the Coalition realized that its continued aggression could spark a greater conflict. The invading Coalition military, while superior in both numbers and technology, was far from any supply centers, and most personnel were genuinely tired of the unchallenging conflict. The ceasefire was accepted by a relieved Judea, and Judea entered the orbit of the United Technocracies.