"Following the conflicts in the late 1990s in the countries of the former Yugoslavia, the prospect of membership in the Euro-Atlantic community and the active presence of the United States in the Western Balkans provided a level of stability that allowed most of the countries of the region to pursue reform and adopt Western values. During this time, Slovenia and Croatia joined the European Union(EU). These countries, along with Albania, also joined NATO. Montenegro became NATO's 29th member on June 5, 2017. Other nations of the Balkans are at various stages on the path toward EU or NATO membership."
CRS Report for Congress, R44955
Congressional Research Service: https://crsreports.congress.gov/