Bricks of the house wall become crumbly, causes being sought

In the basement of my house (about 70 years old) there are some walls made of red brick. I have noticed that these bricks show severe cracking and the surface is literally disintegrating. The bricks seem to be crumbling. Where does this come from and how can I stop it?

This dissolution of the bricks is due to moisture. The basement is probably not sealed from the outside, so water can penetrate; it doesn't have to be a large amount, consistent dampness over the decades is enough. The best solution would be to seal the basement walls from the outside. Since this is often not possible afterwards (e.g., if the house is not completely free-standing), there are injection and consolidation measures carried out by specialist companies. If you enter "Ziegelsteine verfestigen" into a search engine, you will find quite a bit on the subject.