The United States sent its highest-ranking military officer to Ankara to limit any damage to relations between the US, Turkey and the rest of NATO. The Chairman of the Joint Chiefs of Staff, Joseph Dunford, assured Ankara that the US would continue to support democracy in Turkey. He condemned the attempted military coup.

It was the same message that the general secretary of the alliance, Jens Stoltenberg, had already given Turkish President Recep Tayyip Erdogan in a telephone conversation two days after the coup attempt. But Stoltenberg also said that Turkey had to respect its own democratic order, rule of law and human rights.

The Turkish government was displeased with what it regarded as this very restrained expression of solidarity. In interviews, Erdogan himself called for high-ranking foreign politicians to visit Turkey. Until now, NATO has not commented officially on the purge of suspected rebels from the Turkish military. The word from Brussels was that it is the right of every NATO member state to replace its own military leadership.

Member since 1952: Turkish flag flies at NATO headquarters in Brussels

Can only democratic states be NATO members?

The preamble of the NATO Treaty refers to democratic values and principles. But during the Cold War the alliance was not so choosy. In 1949, when it became a NATO founding member, Portugal was ruled by a dictator. Over the course of NATO's history, its members Turkey and Greece have from time to time been ruled by the military following coups.

How important is Turkey to NATO?

The US Air Force maintains a large airbase with around 2,000 troops at Incirlik near the town of Adana. It serves as a base for airstrikes on positions of the 'Islamic State' group in Syria and Iraq. Incirlik played an important role in the wars in the Persian Gulf and NATO's Afghanistan mission. Around 250 German soldiers with Tornado reconnaissance planes and a refueling aircraft are also temporarily stationed there.

Incirlik is not a NATO facility. But the western Turkish port city of Izmir hosts one of the five NATO headquarters, which is responsible for coordinating major operations of land-based forces. The Allied Land Command, or LANDCOM, is subordinate to the NATO Supreme Allied Commander Europe. There is also an important US military airport in Izmir.

A German reconnaissance plane heads to Incirlik in Turkey for a Syria mission

Overall, it is estimated that facilities at 20 locations in Turkey are at least partly used by NATO forces. The Turkish army is the second largest military in NATO after that of the US. The Turks have been involved in all NATO operations in Afghanistan, the Balkans, Syria and Libya. In addition, NATO has recently installed a missile defense radar system for Europe in Turkey.

Geopolitically, military experts say Turkey plays an extremely important role as it flanks the trouble spots in the Middle East and the Black Sea. But that should not be overstated, says the former Chairman of the NATO Military Committee, retired German General Harald Kujat. Turkey, he said on German public radio, has always been an ally on which one cannot rely 100 percent. He described Ankara's role in the fight against "IS" as "dubious" - at least initially.

Is the future of Incirlik in question?

Erdogan has loudly demanded that the US extradite cleric Fethullah Gulen, whom he considers the mastermind of the recent attempted coup. US authorities say they will consider the petition once Turkey submits evidence. Gulen, who lives in Pennsylvania, denies any connection to the coup.

Two years ago, Turkey granted the US the right to use Incirlik for airstrikes against "IS." Ankara could now use the base as leverage in the dispute over a potential extradition of Gulen. The government in Ankara has also criticized the US for its support of Kurdish groups in the struggle against "IS" in Syria. It considers these Kurds terrorists.

Turkey is also involved in a feud with NATO member Germany about a parliamentary resolution on Armenia. Earlier this year, the Bundestag recognized the Armenian Genocide in the Ottoman Empire a century ago, which Turkey vehemently denies. German parliamentarians are therefore currently banned from visiting German soldiers in Incirlik. If this does not end soon, parliament could withdraw German soldiers from Turkey.

Can NATO expel or punish Turkey?

The North Atlantic Treaty makes no mention of leaving or being expelled from the alliance, nor of any penalties for misbehavior. The treaty can only be terminated by the member state itself.

The importance and service capability of the Turkish armed forces in NATO is likely to decrease, former NATO Supreme Allied Commander in Europe James Stavridis said. "Unfortunately, it is likely that the military in the wake of the coup will be laser-focused on internal controversy, endless investigations, and loyalty checks - and simply surviving as an institution. This will have a chilling effect on military readiness and performance," he wrote in "Foreign Policy" magazine.

Stavridis said the military will have to struggle to maintain its authority in the Turkish state. "This will have a chilling effect on military readiness and performance. While some operations have resumed at the crucial Incirlik Air Base, cooperation is already frozen across many US and NATO channels," he warned.