ON Wednesday, it was exactly 76 years since Russian soldiers reached Auschwitz concentration camp ­— and the full horror of Nazism was revealed to the world.

We knew that the Jews were being persecuted and other camps had already been liberated, but this was murder on an industrial scale.

Around 1.5 million of the Nazis’ several million victims died in Auschwitz.

Auschwitz is now a UNESCO World Heritage Site, though not for the same reasons as the Lake District. The national park won the status for its extreme beauty. Auschwitz got it for its extreme ugliness.

The other way that anniversary is marked is with Holocaust Memorial Day. It has been held on January 27 every year for the past 20 years.

This year’s commemoration was a scaled-back event ­— as so many things are these days ­— but the evil it asks us to remember is as huge as ever.

The victims weren’t just Jews but Slavs, Gypsies and others who didn’t fit within the Nazi notion of a German “master race”.

There were also “undesirables”, who included gay people, disabled people, those with mental illnesses and political opponents such as communists, socialists and trade unionists.

Even Jehovah’s Witnesses and Esperanto speakers found themselves in concentration camps.

We are told it is important to mark Holocaust Memorial Day to ensure that it never happens again. Yet persecuting and killing people for their race, beliefs or lifestyles still goes on. Thousands were murdered in Cambodia, Bosnia, Rwanda and Darfur because of who they were.

And don’t forget northern Iraq. Many people opposed the Iraq War, but it’s worth noting that the Kurds didn’t.

They were the victims of attempted genocide by Saddam Hussein, with thousands tortured, raped and murdered or maimed and disfigured by mustard gas.

At this very moment, the Muslim minority in north-west China called the Uighurs, are being persecuted and incarcerated because of their religion. If anything, genocide has increased over the past 76 years.

That is why we always have to be alive to the dangers of discrimination on the grounds of race, religion, beliefs of sexual orientation. We can’t forget what it can lead to.

People who used to be sneered at for being “politically correct” are now regularly denounced as “woke” ­— as if there was something good about being sleepily unenlightened.

I’ve never seen political correctness or “wokeness” as things to be entirely dismissive about. Much of the time, it’s no more than common courtesy.

Isn’t it more polite and sensitive to say that someone has mobility problems than to call them a cripple? When women serve in the police and fire brigade, isn’t it better to call them officers and firefighters rather than policemen and firemen?

If that make me woke, politically correct or a bleeding-heart liberal, that’s fine by me.

We all need to be wide awake to the dangers of discrimination, even at football matches.

Since the start of the last season, some players have chosen to “take a knee” at the start of games to show their support for racial equality.

Many Millwall fans booed their players for doing so. But what harm did it do, other than delay kick-off for a couple of minutes?

Showing contempt for the gesture is to suggest that racial hatred isn’t something wrong and dangerous.

For centuries, the Jews in Europe were resented or treated with suspicion. Even a socially-aware writer like Charles Dickens could paint an unsavoury portrait of Jews in the character of Fagin in Oliver Twist.

That millennia-old resentment flared up into something horrific in the 1930s. And don’t think Nazism has gone for good or is confined to certain countries.

Thomas Mair, who murdered MP Jo Cox in June, 2016, had links to National Alliance, a white supremacist and neo-Nazi organisation.

The pro-Trump mob who expressed their national pride by ransacking the Capitol building in Washington included members of a whole series of American far-right groups, such as “The Proud Boys”.

Perhaps the most chilling image of the whole incident was of a rioter whose shirt bore the German motto “Arbeit macht frei” ­— “work makes you free”. It was displayed above the entrance gate at Auschwitz.

There is a direct line from casual hatred of people because of their race or beliefs to the greatest crime of the 20th century.

There’s no guarantee that genocide won’t turn out to be a great crime of the 21st century.

That’s worth bearing in mind before we dismiss anyone as “woke” or any anti-racism campaign as “political correctness gone mad”.