Complex sentence: These cadets were the official youth organization within the Puerto Rican Nationalist Party, and were also known as the "Ejército Libertador de Puerto Rico" (The Liberation Army of Puerto Rico).
Split into simpler sentences: These cadets were the official youth organization within the Puerto Rican Nationalist Party. The quasi-military organization were also known as the "Ejército Libertador de Puerto Rico" (The Liberation Army of Puerto Rico).