Istanbul — Turkey's national elections will be decided by a runoff vote as President Recep Tayyip Erdogan faces a the toughest test of his long political career. With nearly all the ballots counted Monday, neither Erdogan nor his chief rival Kemal Kilicdaroglu had secured more than the required 50% to win outright and a national election official said they wouldn't, so a second round of voting was to be held in two weeks.

Erdogan was applauded during his first decade as leader for transforming Turkey into an economic and political success story, but over the last 10 years he's faced mounting criticism — both domestically and internationally — for quashing dissent and adopting rules and laws typical of autocratic regimes.

Once a poster child for developing nations, Turkey is also currently battling high inflation and a cost-of-living crisis, both of which are regularly blamed by opponents and economists on Erdogan's unorthodox economic policies.

Erdogan's chief rival, KiIicdaroglu, is a secular social democrat politician who has emphasized messages of freedom and democracy on the campaign trail. The opposition alliance he represents has promised to roll back constitutional changes introduced after a 2017 referendum that significantly expanded the powers of the presidency, and to bring back the parliamentary system.    

To win the election outright a candidate must secure more than 50% of the votes. Polling suggests that's unlikely, so the nail-biting race between the two leading candidates could easily carry on to a second round of runoff voting, which would be held on May 28. 

Below is a look at why Turkey's national elections are being followed closely around the world.

NATO expansion

Turkey is a member of the NATO military alliance, and it has the second-largest army among all 31 members, behind only the U.S. But relations between Ankara and its NATO partners haven't always been smooth.

Last year, Erdogan frustrated his allies by blocking Sweden and Finland's bids to join the alliance, which were prompted directly by Russia's invasion of Ukraine. Although Turkey lifted its block on Finland's accession last month, allowing the country to join, talks with Sweden fell through.

Erdogan argues that Sweden doesn't take Turkey's domestic security concerns seriously and provides refuge to militants from the Kurdistan Workers' Party, a banned group that's fighting an insurgency against the Turkish state.

Unal Cevikoz, a senior aide on foreign affairs to Erdogan's challenger Kilicdaroglu, told CBS News the opposition alliance has noted "positive steps" taken by Sweden concerning Turkey's security concerns, and it hopes the Nordic nation's NATO membership won't be delayed "too much," signaling support for the Swedish accession bid.

Turkey-U.S. ties

Located on the very border between the Eastern and Western worlds, Turkey is a strategically significant ally and partner for the U.S. unilaterally as well as in the context of NATO.

Relations between the two countries spiraled downward after Turkey purchased S-400 long-range missile systems from Russia in 2019, however, and there have been other points of contention. 

The U.S. said the missile purchase would endanger American military technology, and hit Turkey with sanctions in response.

In the Syrian civil war, firm U.S. support for Kurdish militants, who were instrumental in defeating ISIS, also proved to be a significant thorn in the side of Turkish-U.S. relations. Turkey considers the Kurdish militias backed by the U.S. terror organizations, and even launched attacks against the groups while the U.S. was working with them on the ground.

Another sore point is Muhammed Fethullah Gülen. The Turkish dissident has lived in exile in the U.S. for years. Turkey alleges that his organization, which it also considers a terrorist group, was behind a 2016 coup attempt and has long demanded that the U.S. hand him over. 

But despite the differences, Erdogan's ruling Justice and Development Party (AKP), has pledged to strengthen ties with the U.S. and ensure tangible steps are taken to resolve all the disputes. 

In an interview with the BBC, Kilicdaroglu said he wants to prioritize relations with the West, rather than Russia.

Turkey as a mediator, and ties with Russia

Erdogan has cultivated a close personal relationship with Russian President Vladimir Putin. Not long after Russia launched its full-scale invasion of Ukraine in February 2022, the Turkish leader declared himself a mediator.

Initial talks hosted in Turkey failed to make any headway, but a deal brokered by the United Nations in 2022 and supervised by Turkey has enabled the export of some 25 million tons of grain from Ukrainian ports to ease a global food crisis. That deal is set to expire in about a week, and Russia has so far objected to its renewal. Turkey remains directly involved in the extremely tense negotiations over the agreement's renewal.

Erdogan has refused to implement Western sanctions against Russia, and trade between the two countries has soared since the Ukraine invasion. Turkey is an energy-poor country, and it helps export Russian gas around the world. Russia is also funding and building Turkey's first nuclear power plant.  

Cevikoz, the aide to Erodgan's challenger, said the opposition alliance did not "approve" of Russia's invasion of Ukraine and, if their candidate wins, they would "continue to facilitate" solutions for the problems between Russia and Ukraine.

Turkey's role in the region

Erdogan's ambitious foreign policy has made Turkey a key player in the Middle East. 

Turkey openly supported some of the rebel factions that battled Syrian President Bashar al-Assad's forces, and it has provided safe haven for Syrian opposition members. But Turkey also occupied portions of northwest Syria in 2019, citing security concerns from Kurdish rebel factions, and still controls a vast area of land where 4.5 million people live.  

Turkey currently has the world's largest refugee population, with some 4 million displaced people living in the country. Most are Syrians, though there are also large number of Iraqis, Iranians and Afghans. The high numbers and Turkey's geographic location have made the country a de-facto gatekeeper for the European Union: Ankara signed a deal with the EU to limit the number of asylum seekers reaching European soil.

But a shift in public opinion on refugees, including rising populist rhetoric against them, prompted Erdogan to take steps towards reconciliation with the Assad regime in Syria.  

Turkey's political opposition has vowed to facilitate the return of refugees to Syria if it comes to power, but it has not provided details on how they would do it.  

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• Turkey
• NATO
• Recep Erdogan