Complex sentence: Gwanggaeto dispatched 50,000 expeditionary troops, crushing his enemies and securing Silla as a de facto protectorate; he thus subdued the other Korean kingdoms and achieved a loose unification of the Korean peninsula under Goguryeo.
Split into simpler sentences: Gwanggaeto dispatched 50,000 expeditionary troops, crushing his enemies and securing Silla as a de facto protectorate of Goguryeo. During his rule, Gwanggaeto subdued the other Korean kingdoms, achieving a loose unification of the Korean peninsula under Goguryeo.