Trevor Taylor, an expert in defence management at the Royal United Services Institute (RUSI) think tank, says countries are responding to the "sense of threat". "You've got a case where Russia has demonstrated a readiness to use force to change the territorial status quo," he tells Sky News. He adds: "The question these days is whether Russia would try to take over smaller parts of Europe - whether that's part of Estonia, or Latvia, whether or that's some kind of incursion towards Poland and so on. "Those possibilities now seem much more real than they did before the Ukrainian attack. "I think many countries will conclude that they need to spend more on defence to try and deter those things and be able to deal with them if they occur."