"I take complete responsibility. I'm running for president of the United States. Look, I should have known what he was talking about," he told CNN's Wolf Blitzer.
"We weren't even talking about it in the context of anything, but that said ... Aleppo is the epicenter of what is happening in Syria."
MSNBC "Morning Joe" co-host Mike Barnicle asked Johnson on Thursday what he would do about Aleppo, a major city in Syria that's been engulfed by the nation's civil war and the refugee crisis.
Johnson said he originally thought Aleppo was an acronym. He hopes his campaign can overcome the flub.
"I hope so because, I'm very aware of the policy," he said Friday.
The former New Mexico governor said the next leader of the US needs to avoid entering conflicts like that in Syria.
"As president of the United States, I would have never gotten in this situation in the first place," he told Blitzer. "I don't think that any time we support regime change that it has resulted in a safer world."
Johnson said the United States has "a responsibility to bring this to an end."
"The only way that this Syrian situation comes to an end is with Russia. And of course, we have the potential conflict with Russia in the air that exists in this situation also."
He continued, "So it's a horrible situation that, in my opinion, can only be brought to an end if we involve Russia directly in bringing about a diplomatic solution to this. Obviously, that would start with a ceasefire."
North Korea said
Friday morning it has tested its fifth and potentially most powerful nuclear weapon and claimed to have successfully detonated a nuclear warhead that could be mounted on ballistic rockets.
"North Korea is the biggest threat in the world today (and) that at some point, these intercontinental ballistic missiles are going to actually work. So obviously, with this test today, the explosion itself, the device itself, is getting more potent. The missiles are flying a little bit further," Johnson said.
He highlighted the importance of including China in finding a solution to the threats.
"The only way that we address this is through China. China recognizes this threat as much as anyone else. They are the No. 1 trading partner of North Korea," he said. "From a diplomatic standpoint, without China, this does not get resolved."
Johnson said the situation is an opportunity for the US to remove its troops from South Korea and work with China to address North Korea's behavior.