On October 28, 1922, amidst the political post-war chaos, close to 30,000 fascists and members of the conservative Italian Nationalist Association marched on Rome to seize power on behalf of Benito Mussolini (who himself had stayed in Milan). The mob could have easily been defeated by the army, and Prime Minister Luigi Facta prepared a declaration of martial law. However, conservative King Victor Emmanuel III refused to sign it because a fascist government would keep the emerging socialists at bay, and he appointed Mussolini prime minister on October 31.

In January 1933 President Paul von Hindenburg (who was no friend of democracy himself) appointed Adolf Hitler (as the candidate of the largest party in the Reichstag) chancellor of Germany after Franz von Papen, former chancellor with dictatorial aspirations himself, assured him that he could be controlled. Following the Reichstag Fire, and just days before the federal election, Hitler ordered all candidates of the Communist Party and a large number of Social Democrats to be arrested as arson suspects whose subsequent absence from the Reichstag paved the way for his power grab. In the election the NSDAP received 43.9% of the vote, but apart from the remaining 94 Social Democrats all deputies were conservatives, ensuring that his Enabling Act ('Law to Remedy the Distress of People and Reich') reached the required two-thirds majority with 444-94 votes.

The dictatorship of Francesco Franco in Spain from 1936 to 1975 would not have been possible without the support from other conservative elements such as the Catholic Church, the military and the monarchists.

Russia's gradual descent into fascism under Vladimir Putin has been abetted by other conservative politicians and parties, first and foremost the United Russia Party.

It is also quite easy to transform a regular conservative party into a fascist one. The Republican Party of the United States had been a run-of-the-mill conservative party until 2015. In 2012 it was joined by Donald Trump with the expressed intention of running for president, and he announced his candidacy in 2015. Initially facing a lot of opposition and ridicule within the party, his racist, homophobic, misogynistic and populist rhetoric appealed greatly to the party's base base, especially white evangelical Christians and, naturally, those who were fascists already. He secured the nomination and went on to win the presidency with not the majority of voters but of electors (which is what matters in the US) in 2016. Using the Mafia-style leadership he had already employed as a businessman, he demanded unquestioning loyalty and severely punished any form of dissent, turning the party into a fascist personality cult. The Republicans who dared to oppose him were too few to form any movement within the party (let alone their own party) and soon disappeared from the scene. After he sent an armed mob to the Capitol to attack Congress, kill his vice president and keep him in power after a lost election in 2021, a handful of Republican Congresspeople denounced him but, after realising that the insurrection had strengthened Trump's grip on the party's base, went back to kiss the ring and even interfered in judiciary processes against him on his orders after he left office.

In conclusion, conservatives don't prevent fascism, they enable it.

In my model of The Neurological Spectrum - Between Individual and Collective Identity I have pointed out how people on the individual end of the spectrum see everybody as an equal, welcome progress and appreciate diversity and individual expression.
On the other hand, people who identify collectively internalise their groups' hierarchies, strive to preserve the status quo (or even revert to a former stage) and consider diversity and individual expression a threat to their 'way of life' (which is a fancy term for the status quo). The one (and only) evolutionary advantage of collective identities is the ability to network which can be seen in the power to summon a bloodthirsty mob whenever a group's privileges are challenged.
Progressives usually identify individually while conservatives tend to identify collectively (in the Western world predominantly as whites, as Christians and as nationalists) and are therefore far more susceptible to peer pressure and command structures.

While the driving force of those who identify individually is hope, the driving force within collective identities is fear - both the fear of not fitting in and the fear of them, whoever they may be, and therefore adherents yearn for an autocrat who'll rule with an iron fist and destroy their perceived enemies. At the same time those in leading positions will look for an intellectually challenged candidate who is both angry enough to fulfil the strongman fantasy of the masses and gullible enough to carry out their own agenda; the second part always fails horribly since the autocrat has no intention of sharing his power with those who handed it to him.