Complex sentence: Fencible units were raised in the United Kingdom during the early years of the war, this included not only land regiments but also the Sea Fencibles (raised in 1798 and disbanded in 1810).
Split into simpler sentences: Fencible units were raised in the United Kingdom during the early years of the war. This included not only land regiments but also the Sea Fencibles (raised in 1798 and disbanded in 1810).