The Blackwater War was a military expansion ordered by Reman II in 1E 2811 - 1E 2837. It seized the northern and eastern marches of Argonia, resulting in the formation of the Imperial Province of Black Marsh. While the Imperial forces won several decisive battles in the early stages, their progress quickly stagnated due to the brutal terrain, endless raids, disease, and mysterious disappearances. After several failed campaigns, each employing wildly differing tactics, the conflict declined into a protracted and complex guerrilla war with no clear victor in sight. Ultimately, tribal infighting on the part of the Argonians finally brought the war to a close. Rather than an official armistice, the war simply ended when the Argonians abruptly buried their weapons and went back to their day-to-day lives.
- Battle of Argonia, 1E 2811. A one-sided affair with Argonians suffering significant casualties. The survivors retreated to Helstrom, the impenetrable center of the Province.
- Xi-Tsei Massacre, Last Seed 14, 1E 2820. The remnants of General Bucco's fourth legion were annihilated by a massive Argonian war party at the foot of an ancient Argonian pyramid.
- Great Burn, Rain's Hand, 1E 2828. In an attempt to neutralize the inhospitable terrain, Elissia Mallicius ordered a unit of sappers to set fire to a peat bog outside of Stormhold. Unbeknownst to the Legion, the fire spread through a vast underground network and within months the entire province was ablaze. Hundreds of species of unique flora and fauna were rendered extinct and entire tribes of Argonians were lost. The Legion suffered significant casualties, this marked the end of their second campaign.