NATO leaders are preparing to gather in London for a two-day meeting Tuesday to mark the 70th anniversary of the establishment of the alliance, but growing tensions among members could overshadow the celebrations.
The war in Syria and the ongoing Russian threat will serve as the backdrop to the summit. Fellow NATO members the United States and Turkey came close to confrontation in northern Syria last month, rattling the alliance.
"The position of Turkey in the North Atlantic alliance is a difficult one," said Jonathan Eyal of the Royal United Services Institute in London in an interview with VOA this week.
"Turkey's decision to become involved in military operations in the Middle East against the wishes of most of its allies, including the United States, [and] Turkey's decision to buy Russian military equipment … [are] riling with many countries in Europe."
NATO members say it's better to have Turkey inside than outside the alliance.
"NATO is about European security, it's not about coordinating policies in the Middle East," Eyal said.
Where American troops once kept the peace, Russian forces now patrol northern Syria. The U.S. withdrawal has fueled concerns over America's commitment to NATO. French President Emmanuel Macron recently called the alliance "brain dead" and urged Europe to create its own security architecture.
The comments elicited a sharp rebuke from NATO Secretary-General Jens Stoltenberg this week.
"European unity cannot replace transatlantic unity. We need both. And we have to also understand that, especially after Brexit, the EU cannot defend Europe," Stoltenberg told reporters.
Europe still sees Russia as the biggest threat following its 2014 forceful annexation of Crimea and ongoing campaigns of espionage, cyberwarfare and disinformation.
European concerns over the U.S. commitment to Article 5 of the NATO treaty, on collective defense, are not borne out by facts on the ground, Eyal said.
"The reality is the Pentagon's spending in Europe is increasing, the number of U.S. troops is increasing."
The deployment of U.S. troops in Europe is seen differently in Moscow.
"Some of the Eastern European nations are trying to get American boots on the ground despite the fact that Article 5 should cover their security, which suggests that they trust the United States more than they trust NATO," Andrey Kortunov of the Russian Council on International Affairs in Moscow told VOA in a recent interview.
U.S. President Donald Trump has repeatedly demanded that European NATO members "share the burden." Germany on Wednesday pledged to meet the NATO defense spending target of 2% of GDP, but only by the 2030s.
"The U.S. president should be credited with actually banging the table hard enough for the United States to be heard," Eya said, "This is, and it's important sometimes to repeat the cliché, the most successful alliance in modern history."
NATO will hope that is cause for celebration as leaders gather for its 70th anniversary.