From the Overview: "Heads of state and government from NATO's 29 member states are scheduled to meet in London, United Kingdom (UK) on December 3-4, 2019; they last met in Brussels, Belgium, in July 2018. Two key goals for the meeting will be to commemorate the alliance's past achievements--2019 marks NATO's 70th anniversary--and to advance efforts to address new and emerging security challenges, including renewed Russian aggression, terrorism, and cyber and hybrid threats. The meeting also could expose heightened political tension within the alliance and divergent views on a range of issues, including U.S. policy toward NATO and Europe, relations with NATO member Turkey, and relations with Russia."
CRS Report for Congress, R46066
Congressional Research Service: https://crsreports.congress.gov/