Complex sentence: Trotsky founded the Red Army with an initial Red Guard organization, and a core soldiery of Red Guard militiamen and Chekist secret police; conscription began in June 1918, and opposition to it was violently suppressed.
Split into simpler sentences: Trotsky founded the Red Army with an initial Red Guard organization, and a core soldiery of Red Guard militiamen and Chekist secret police. Conscription began in June 1918, and opposition to it was violently suppressed.