How did King Taejo eliminate his competitors?

He sent them into exile.

He had them killed.

He turned them into slaves.

He made them become priests

The answer is: "He had them killed."

Explanation:

King Taejo (1392-1398) was also known as "Taejo of Joseon" or "Yi Seong-ge" of Korea. He started as a successful general in his career. He only became king after eliminating his competitors, by secretly having them killed.

For example, when King Gongyang (Yo) became the King, he allied with some aristocrats in order to overthrow him. It was an easy task for him because "Yo" acted like a puppet king for him. When he took over the throne, he issued an order to put King Gongyang and his family into exile. However, it is said that he actually secretly have all of them killed.

Another incident occurred when King Taejo ordered the killing of Jeong Mong-ju, a scholar and diplomat who was a prominent figure during those times. He had him murdered while he was on his way home, after attending a party. The reason behind this was that, Jeong didn't like the ruling of King Taejo and had always opposed him.

Thus, this explains the answer.