The German Lutheran pastor Martin Niemöller is credited with these famous postwar lines:
First they came for the Communists, and I did not speak out—because I was not a Communist. Then they came for the Socialists, and I did not speak out—because I was not a Socialist. Then they came for the trade unionists, and I did not speak out—because I was not a trade unionist. Then they came for the Jews, and I did not speak out—because I was not a Jew. Then they came for me—and there was no one left to speak for me.
In the realm of international relations, this tragic and cautionary tale could be titled «Isolationism». Doing nothing is often, in its own way, an action. President Barack Obama, for example, chose in August 2013 to do nothing in Syria, despite having promised to intervene if the Assad regime used chemical weapons. We are still experiencing the consequences of that inaction.
The fruits of isolationism
It is plausible that this display of weakness emboldened Putin to invade Crimea and Donbas and to intervene in Syria's civil war. Russia's aggression against Ukraine led, eight years later, to a full-scale war.
The Syrian civil war and Russia's support for a murderous regime have caused the deaths of 400,000 Syrians and displaced millions to Lebanon, Jordan, Turkey, and Europe. The resulting refugee crisis has redrawn the internal political landscapes of many EU countries. Additionally, Iran's influence in Syria and Lebanon has grown, leading to continued destabilization of Lebanese politics and the strengthening of Hezbollah, and so on and so forth.