(CNN)- I teach my students that foreign policy is persuading other countries to do what you want. The tools available to accomplish this include everything from kind words to cruise missiles. Mixing them properly and with sufficient patience is the art of diplomacy, a task that for the United States has proved challenging even with our closest allies, and altogether necessary with the Islamic Republic of Iran.

The United States and Iran have been locked in an adversarial relationship since the 1979 hostage crisis. Having worked for President Jimmy Carter, I viewed the country through the prism of that experience when I served in the Clinton administration. Nevertheless, as secretary of state I felt it important to explore the possibility of developing a less chilly relationship with Iran.

During my time in office, we offered to engage in dialogue, but the Iranians were not ready. In the end, although we improved the relationship on the margins, we failed to make much of a dent in the thick wall of mistrust separating our two countries.

These experiences lead me to be wary of the Iranian regime and realistic about the prospects for an overnight change in U.S.-Iranian relations. But it is dangerous not to pursue dialogue, and experience convinces me that the nuclear agreement between world powers and Iran is a wise diplomatic initiative.

After careful review of its provisions, I have given the Joint Comprehensive Plan of Action my strong endorsement.

The prospect of a nuclear-armed Iran has rightfully earned a place at the top of the long list of threats to global stability. No diplomatic agreement or military action could guarantee that Iran will never obtain a nuclear weapon, but even most opponents agree this accord puts that goal firmly out of Iran's reach for a decade or more. From any vantage point, that is a positive development, but at a time of great turmoil in the Middle East it is especially welcome.

One of the main criticisms that has been leveled against the JCPOA is that it does not address other abhorrent aspects of Iran's behavior -- its support of terrorism, its jailing of several Iranian-Americans, its rhetoric against the United States and Israel or its other destabilizing activities in the broader Middle East. In theory, the United States could have pursued a comprehensive agreement with Iran covering issues beyond the nuclear file, but experience suggests that such an approach would not have yielded results.

By CNN