Complex sentence: A disastrous first-contact with the Minbari in the 2240's, however, precipitated the Earth-Minbari War, in which Earth was nearly conquered; however, the Minbari mysteriously surrendered just prior to the final invasion of Earth.
Split into simpler sentences: A disastrous first-contact with the Minbari in the 2240's precipitated the Earth-Minbari War, in which Earth was nearly conquered. However, the Minbari mysteriously surrendered just prior to the final invasion of Earth.