This is quite a big 'WI' but its not one that we ever discuss too much (unlike 'nazis win ww2', 'cp win ww1', etc...)
So...assume during the late 15th century there is a Pope who cares who does a bit of reforming from within and pushes the catholic church towards how it was IOTL post-Trent. As a result there's no Lutheranism or Calvinism or anything like that.
I suppose you could assume a few more Husses in the years that follow but nothing with such a large impact as OTL protestantism.
How would civilization develop without this huge event?
I have my ideas....