In the last year in particular, the movements known as the "alt-left" (alternative left) and the "alt-right" (alternative right) have been gathering considerable momentum, especially in the USA and the UK.
The alt-right became popularised and invigorated by the election of controversial US President Donald Trump in 2016, especially when Breitbart editor Steve Bannon was notoriously appointed to Trump's presidential cabinet. "Men's rights activists" like Milo Yiannapoulos, much hated by feminists and left-wing students on both sides of the Atlantic, and racist Eurosceptic parties like Alternative fur Deutschland (AfD) and the Sweden Democrats (SD) have been gathering more momentum and more credibility than ever. The alt-right is a new kind of racist right, using various excuses like possible terrorist threats and playing on general anti-immigration feelings to spread hate and fear to any who will listen, and incite hatred and violence towards innocent people simply because of their religion or race.
The alt-left, meanwhile, started out on student campuses across prestigious universities in the USA, latterly spreading to the majority of campuses in the UK and particularly amongst student union activists. The advance and expansion of social media platforms, especially Facebook and Twitter, which appeal to those under the age of 30 most, has enabled this movement to flourish and make a real impact in internal politics, especially in the UK. "Identity politics" and "intersectionality" are key parts of the alt-left movement, and their interpretations of both make it just as oppressive as the alt-right, albeit in different ways. Moderate feminists like Germaine Greer are routinely censored and attacked by the more radical feminists comprising much of the alt-left.
Although much of the news relating to the latest exploits of the alt-left and alt-right is from the USA and the UK, the movements are also expanding to a lesser extent in continental Europe.
Both the alt-right and alt-left movements are cult-like in many ways. They are authoritarian, intolerant of any kind of dissent, very secretive in many ways, and have no qualms about hijacking legitimate and plausible groups of parties to enforce their ideologies. Liberal students on US and UK university campuses frequently speak of being driven out, shunned or unfairly excluded as a result of the actions of alt-left student activists, who use "safe space" policies, extreme and often outright ridiculous interpretations of (sexual) harassment (e.g. a belief that even looking at a woman the wrong way somehow constitutes sexual harassment even when the look was in no way sexual), and make accusations of "cultural appropriation" and "oppression" towards many reasonable people who just don't happen to share the alt-left's extreme views on identity and culture, who do not approve of unreasonable censorship, and who don't think pulling down historical statues makes sense even if the statues were of historical oppressors like Cecil Rhodes. Meanwhile, the alt-right routinely incites believers toward notably Islamophobia, misogyny, anti-Semitism, racism, and transphobia, and cruelly mocks minorities and vulnerable groups.
Both of these movements are dangerous because their authoritarian, aggressive, and secretive nature can pose a real threat to basic freedoms and human rights, which are crucial to modern and functional human societies. It is therefore crucial in these difficult times that both the alt-left and the alt-right movements are countered and defeated, to preserve fundamental human rights and freedoms, and to protect democracy from being subverted and warped into dictatorship the way so many were in the 1920s and 1930s. They may seem like fads for now but they will not simply fade away like clothing fashions; they must be dealt with especially in this divided and somewhat confused world of ours. To paraphrase Winston Churchill, "Democracy may be the worst form of government, except for the fact we've tried all the others."
Keep calm and carry straight on for common sense.