What you need to know about the U.S.-Iran nuclear deal

WATCH: After nearly two years of tense talks negotiators emerged from closed-door discussions Tuesday with a deal to curb Iran’s nuclear program in exchange for relief from international sanctions. Craig Boswell reports.

United States President Barack Obama announced Tuesday morning that after 18 days of intense and sometimes fractious negotiations, world powers and Iran had agreed to curb Iran’s nuclear program.

The accord will keep Iran – the country the United States has called the “leading state sponsor of terrorism” – from developing enough material for a nuclear weapon for at least ten years, Obama said.

Why did negotiations come about?

The agreement, the so-called Joint comprehensive Plan of Action, is designed to avert a nuclear-armed Iran and another U.S.-led intervention in the Middle East – that’s America’s win.

Iran, for its part in the deal, sought to have some economic conditions which had been placed on the country by the United Nations, removed. And that benefit has the potential to be massive for the country and include access to more than $100 billion in assets frozen overseas, an end to a European oil embargo,  as well as financial restriction on Iranian banks.

WATCH: US Secretary of State John Kerry has outlined the details of an historic deal struck on Tuesday to curb Iran’s nuclear programme.

Iranian Foreign Minister Mohammad Javad Zarif called the 100-page agreement a “win-win solution.”

What’s included in the deal?

As part of the agreement, Tehran agreed to a continuation of a UN arms embargo on the country for up to five more years. However that embargo could end earlier if International Atomic Energy Agency (IAEA) investigators conclude the country has stopped all work on nuclear weapons.

A UN restriction on the transfer of ballistic missile technology to the country continues for up to eight more years.

WATCH: Obama says that because of this deal Iran can’t make nuclear weapons.

The American government was keen to extend these bans, concerned that the country might expand its military assistance for Syrian President Bashar Assad’s government, Yemen’s Houthi rebels, the Lebanese militant group Hezbollah and other forces opposed to American allies like Saudi Arabia and Israel.

Iranian negotiators also agreed to respond to requests to open their borders to UN and IAEA inspectors, however access isn’t guaranteed and the country’s supreme leader Ayatollah Ali Khamenei had long vowed to oppose allowing inspectors to tour military sites.

Read the deal

The origin story

Negotiations had been led by the United States since it joined in 2008, but British, Chinese, French, German, and Russian officials also played a part in the negotiations which had been running on and off for nearly a decade.

Breaks in the negotiations sometimes lasted for months, and in the ensuing decade Iran’s nuclear program expanded into one that Western intelligence agencies thought was only months away from developing weapons.

That changed in 2013 when Hassan Rouhani was elected president and stated publicly that his country was ready for serious talks.

That’s when the negotiations, frequently marked by failure, made significant progress towards Tuesday’s deal. In September 2013, Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif met at the United Nations and President Obama had a telephone conversation with his Iranian counterpart Rouhani.

So what happens now? Further – domestic – negotiations

WATCH: U.S. President Obama said that a world without a nuclear deal with Iran is a much more dangerous place and that he would veto any resistance from Congress because saying no to the deal would be ‘irresponsible.’

Though Obama’s political opponents have already been criticizing the negotiations, now that a deal has been reached, the president’s team has to sell the deal to Congress.

The Republican-controlled Congress has a 60-day review period during which Obama can’t actually follow through with any of the concessions he made.

The Republican congress could also vote down the agreement and that’s where it gets tricky.

Obama has said he would veto any move by Congress to block the deal but Congress could override that veto with a two-thirds majority vote. That, however, seems unlikely as House Speaker John Boehner has already said he doesn’t think critics of the deal could rally those votes.

WATCH: Iranian President Hassan Rouhani said “a new chapter” had begun in relations with the world and the Islamic Republic

READ MORE: U.S. Senate Republican leader predicts Iran nuclear deal will be ‘hard sell’

And Israel – a key ally of the U.S. in the Middle East – has already exhibited deep suspicion of the deal.

Israeli Prime Minister Benjamin Netanyahu said in a statement Tuesday that the deal is a “bad mistake of historic proportions” and would enable Iran to “continue to pursue its aggression and terror in the region.”

Some Iranian politicians also oppose the deal that would force the country to dismantle a program they’ve spent billions of dollars developing.

• With files from the Associated Press