There were a lot of things he did to turn the Republic into a dictatorship, but the main one was after a war. Consuls in the Roman Republic are given a bunch of troops in times of war who pledge loyalty to them, and are expected to give them back after the war is over so they don't try taking over the government. Caesar and Pompey were consuls, and after a war, Pompey handed over his troops, but Caesar refused and killed Pompey. For the next few years, he worked to take apart the Republic and was ultimately assassinated (too late) because senators feared he had too much power. Unfortunately for them, his step-son Augustus took over and became the first emperor of Rome, officially killing the Republic once and for all.
