Donald Trump described his foreign policy as an "America first" approach that will stop the US from being systematically "ripped off."
The Republican frontrunner, who has spent his entire career in business, gave the most in-depth discussion so far on foreign policy in a phone interview with the New York Times.
During the conversation, he detailed his views on issues ranging from East Asian security to Syria, the Islamic State group and relations with allies such as Saudi Arabia.
Trump said he was not an isolationist, but described the United States as a poor debtor nation that disproportionately funds international alliances such as NATO and the United Nations.
Similarly lopsided relationships exist with allies such as Japan, South Korea and Saudi Arabia, he said.
"We have been disrespected, mocked and ripped off for many many years by people that were smarter, shrewder, tougher," he told the Times.
"So America first, yes, we will not be ripped off anymore. We're going to be friendly with everybody, but we're not going to be taken advantage of by anybody," he said.
Trump slammed President Barack Obama's administration for seeking a political exit for Syrian President Bashar al-Assad while simultaneously fighting the Islamic State group as "madness and idiocy."
"I'm not saying Assad is a good man, 'cause he's not, but our far greater problem is not Assad, it's ISIS," he said.
The real estate developer said he would instead target the oil that provides a significant portion of the extremist group's funding, cracking down on underground banking channels to cut off the flow of money.
Trump, who has repeatedly called for Middle Eastern allies to contribute boots on the ground in the fight against IS, said he would "probably" stop buying oil from countries like Saudi Arabia unless they did so or reimbursed the United States for its role in the fight.
He also said he would withdraw US troops from Japan and South Korea unless the two Asian countries significantly increased their contributions to Washington for the military presence.
"We cannot afford to be losing vast amounts of billions of dollars on all of this," he said.
Asked if Japan should be allowed to have nuclear weapons to protect itself from North Korea, Trump suggested that would be an acceptable situation.
"Would I rather have North Korea have them with Japan sitting there having them also? You may very well be better off if that's the case." he said.
Trump added that he got most of his foreign policy information by reading various newspapers including the New York Times, which released a full transcript of the interview.