Terraforming War or Terraforming Wars were a significant conflict in the Seleschul system frequently referenced in the strip.
While the exact cause, duration, results of the Wars, or even who exactly was fighting whom have not been explained yet, the Wars seem to be the most notable event in recent Seleschul history. No one mentioning them has ever bothered to explain these details, so they are likely common knowledge. Captain Kaff Tagon 2003-02-22, General Karl Tagon 2012-10-07, Lieutenant Commander John Der Trihs2005-08-18, and, presumably, Chief Warrant Officer Gunther Thurl served in Terraforming Wars.
The Terraforming War (singular) is first mentioned by Kaff Tagon in a conversation with Schlock on 2003-02-22, and later as Wars (plural) on 2005-08-18 and 2006-03-10. Karl and Kaff Tagon's tragic back story revolves around the opening salvo of the war as shown on 2012-09-30, 2012-10-07, 2012-10-14, and 2012-10-21
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Judging by Captain Tagon's age and career, the Wars ended some 20-23 years before Sergeant Schlock enlisted with the Toughs. Coming from a military family, Tagon likely enlisted at the earliest possible age, and after four years in infantry would have been around 22 at the beginning of hostilities. If that assumption is correct and if the notes from Howard's private Wikidpad are still canon, and Tagon was indeed 45 when his company was purchased by Breya and Kevyn. the wars took place some time between 3072 and 3075.