The improved diplomatic relationship between the United States and Iran reduces the chances of military conflict, according to an expert on the issue.

Author and historian David Crist is in Tucson this week to speak to the Tucson Committee on Foreign Relations, and says the recent agreement for Iran to reduce its nuclear capabilities in exchange for reduced financial sanctions is "probably the most progress we've had on nuclear talks in 10 years and perhaps the most significant breakthrough in U.S.-Iranian relations in 35 years."

He attributed the notable changes to the new Iranian President Hassan Rouhani, and said the breakthrough in relations is a "confidence building measure."

The agreement between six European countries, the U.S., and Iran, calls for the Middle Eastern country to cap its nuclear program so it cannot produce the type of energy necessary for a nuclear weapon, and increase inspections at uranium mines so the country can not divert mined material for weapons use. In exchange, western countries agree to lift $7 billion in economic sanctions against Iran.

"It buys time until we can finally negotiate a permanent agreement," Crist said.

Iran has already started reducing its nuclear program, which is a good sign. The impacts of a negative relationship with Iran are no less than war, he said.

"There's no more significant foreign policy program than Iran and its nuclear program," he said. "I believe it is probably the greatest potential cause for military conflict for the United States."

Crist is author of the book "Twilight War," about the U.S. relationship with Iran. He used the word "twilight" to explain the relationship because he said it is between peace and war, in between friend and foe.

"It's a relationship that has ping-ponged back and forth between the hopeful prospect of peace and dialogue and also the very likelihood of war," Crist said.

Ultimately, the agreement comes down to how each side carries it out.

"The Iranians have repeatedly stated that they have no intention of a nuclear weapons program, whether that's true or not, we're not quite sure," he said, but the country is making an effort. "So far the Iranians have adhered to at least the early parts of this plan of action."

From Crist's perspective, the U.S. and European countries in the deal have kept up their end of the deal. Only time will tell whether that continues to be the case for all other aspects of the agreement, he said.