Complex sentence: However, Colonel Segismundo Casado joined by José Miaja, Julian Besteiro and Cipriano Mera tired of fighting which they regarded then as hopeless and seeking better surrender terms, seized power in Madrid on 5 March 1939, created a National Defense Junta and deposed Negrín.
Split into simpler sentences: However, Colonel Segismundo Casado, joined by José Miaja, Julian Besteiro and Cipriano Mera, tired of fighting, which they regarded then as hopeless. Seeking better surrender terms, they seized power in Madrid on 5 March 1939, created a National Defense Junta, and deposed Negrín.