Second, we must show the aggressor that we are ready to defend ourselves and, if need be, to fight. Sometimes the best way to achieve peace is to be willing to use military strength.

To do so, we need to strengthen our collective defense, especially on the alliance’s eastern flank that borders Russia. That’s why in Estonia we are increasing the amount we spend on defense. This year, we’ll spend 2.3 percent of G.D.P.; in the coming years, that will rise to 2.5 percent. All NATO countries, irrespective of their location, should do the same: Two percent of G.D.P. must become an absolute minimum requirement. By increasing our spending individually, we can ensure we are all collectively safer.

We at NATO have a solid basis to work from. Members are committed to the defense of the whole of NATO territory, and in recent years the alliance has taken some bold, necessary steps. Among them was the establishment in 2016 of an enhanced forward presence of allied troops — multinational, combat-ready battle groups — in Poland, Lithuania, Latvia and Estonia. On Wednesday the alliance announced that it will likely double the number of battle groups on its eastern flank.