You can think of it in terms of hacking. Western democracies are especially vulnerable to some forms of attacks. Corruption means that politicians can be bought (or threatened with compromat). If the population is angry and you keep lying to them they will have mistrust for media. If you have potentially problematic high immigration and mainstream parties ignore it, it´s easy for someone else to come and fill the niche. (here in Spain we now have a new leftist anti-immigration party to fill the obvious niche, for example).
These vulnerabilities can be hacked. Russia, China, Iran, Israel, whoever wants to exert influence can exploit these vulnerabilities. If you have the breeding ground for unrest it´s reasonable to expect they will exploit it. Just like we don´t get angry at, and often even reward the hacker who detects these vulnerabilities, I beg you not to get angry at me for pointing out the vulnerabilities that the right wing exploits in Europe. Would you get angry at me for pointing out that the corruption of politicians enables the rise of populist right wingers? Like it happened with Trump? Well, now that I think of it many of you ideological blindered posters probably will. No sense of self criticism whatsoever...