From reluctance to reassurance: Explaining the shift in the Germans' NATO alliance solidarity following Russia's invasion of Ukraine

Russia's invasion of Ukraine in 2022 has led to a shift of public opinion in Germany on collective defense: reluctance towards the defense of NATO's eastern flank has given way to majority support for military efforts to reassure NATO's eastern members in the face of Russian aggression. Against the background of the war, which factors are driving this shift in peoples' alliance solidarity? An in-depth analysis of representative population surveys from 2021 and 2022 shows that the perception of Russia as a security threat is the key factor, yet it is only part of a more complex explanation involving peoples' strategic postures and issue-specific knowledge as well. Contrary to common belief, a free-riding mentality turns out to be irrelevant. The empirical findings shine light on Germany's reaction to Russia's war against Ukraine and add to our understanding of the societal foundations of alliance solidarity in Germany and other NATO countries.