Diplomacy's great promise is that one can never predict where discussions will lead once they have begun. Serious, sustained negotiations first produced a historic nuclear deal between the U.S. and Iran. They continued working together to ensure that 10 American sailors were released from Iranian custody less than 24 hours after inadvertently crossing into Iran's territorial waters. And now, high-level negotiations have led to the release of four Americans imprisoned in Iran in exchange for Iranians imprisoned in the U.S. The positive impact that diplomacy is having on human rights cannot be overstated. Sustaining this momentum will be critical.

For me, the release of these prisoners is personal. As I've written in these pages before, Jason Rezaian is my friend. He never should have been imprisoned in the first place, and after a year and a half, he has finally been reunited with his family. Imagine for a moment that your friend or family member was unjustly imprisoned, and it should be clear for all to see that this was the right thing for the Obama administration to do. Period.

This prisoner release personifies the persistence and wisdom of the Obama administration's diplomatic efforts. It simply could not have happened without dialogue between the U.S. and Iran. The nuclear deal helped begin that dialogue and create the political space necessary for prisoners to be freed. Like the release of 10 U.S. sailors, this exchange is a direct result of the nuclear deal. In Washington, Iran hawks on both sides of the aisle, as well neoconservatives who dominate the Republican foreign policy establishment, will no doubt try to downplay this fact.

This prisoner release personifies the persistence and wisdom of the Obama administration's diplomatic efforts.

As their off-the-handle responses to this past week's U.S. sailor incident show, they will likely try to claim that nuclear negotiations prevented a prisoner release from happening sooner. This couldn't be further from the truth. Two of the four Americans now released from Iranian custody were imprisoned long before serious nuclear talks began in 2013. These two exceptions were unjustly imprisoned because of political disputes in Iran that have nothing to do with them. As the old saying goes: When the elephants fight, it's the grass that gets trampled.

The Obama administration deserves a ton of credit. It had the patience and vision to disregard the aforementioned domestic political circus, absorb the inevitable backlash and prioritize doing what it knew was right. Think about it: Why are hawks complaining at a time when American citizens have been freed from Iranian prison cells and reunited with their families? Shouldn't their safety and freedom be the top priority? Obama's team once again took the necessary diplomatic steps that provide the best hope for a better future. In doing so, the human rights of American prisoners were restored.

This prisoner release is also another important step in the long journey to improve human rights in Iran. First and foremost: War is the ultimate human rights abuse, and thanks to the nuclear deal, that worst possible outcome has been averted. Building off that, the human rights of Iranian citizens have been restored now that they are free from American prison. However, winning the long game on human rights issues in Iran requires far more patience than today's 24-hour news cycle provides.

This exchange is a direct result of the nuclear deal.

Make no mistake: The human rights situation in Iran is far from acceptable. The Iranian government must take more steps to improve the treatment of its own citizens. To achieve a systemic shift in Iran's human rights record, much more is needed, but an important first step is re-establishing communications. Absent direct dialogue, Washington is unable to impact the trajectory of such changes.

Many of us anticipated the challenge Iranians now face. As I wrote with Trita Parsi in 2010, "An Iranian opening to the U.S. will likely be accompanied with a tightening of domestic restrictions as the government will not want its policy to be understood as a sign of weakness." This is precisely the dynamic in Tehran today.

Iranian civil society understands this better than any Washington-based pundit, and that's a major reason why they supported the nuclear deal from the outset. More generally, they glance at the surrounding region and see that violent change rarely improves human rights, while gradual, indigenous reform has a slower but greater chance of success. More specifically, their recent experience shows that when U.S.-Iran tensions increase, so too does their government's domestic crackdown. When Washington and Tehran take steps to de-escalate tensions, they gradually enjoy more breathing room.

It simply could not have happened without dialogue between the U.S. and Iran.

This prisoner release is a small but important example of the impact that U.S.-Iran dialogue can have. As relations between Washington and Tehran slowly thaw, it forces the Iranian government to look inward and address its own shortcomings rather than blame foreign powers. This helps improve the ability of Iranian moderates, pragmatists and civil society to hold their government accountable.

To recap: diplomacy -- not bluster, bombs or bullets -- has produced the most rigorous nuclear deal in the history of the world; safely returned in record time 10 American sailors who inadvertently crossed into Iran's territorial waters; and reunited four Americans imprisoned in Iran with their families. All of this happened in two years. And it doesn't have to stop now. More is possible. The echo chamber of hawkish, disproven voices in Washington cannot change this undisputed truth: The freedom of four American prisoners is yet another triumph of U.S.-Iran diplomacy. What a time to be alive. Welcome home, gentlemen.

PHOTO GALLERY Historic Iran Deal