Avoiding WWI and WWII should already do it IMHO.
Actually avoiding WWI should already do much. Prior to WWI, many European countries showed significant population growth and prosperity. If that had continued, you'd likely have a more conservative setting with higher population growth than IOTL plus millions of dead avoided plus the possible kids of those who died IOTL.
I'd also assume that a continuing "belle epoque" should preserve the traditional conservative elites much more than IOTL, leading to a more conservative Europe with higher population growth.
Then you should also avoid the Russian revolution. Without WWI, WWII, Stalin and the Soviet Union Russia alone could contribute 100 million additional Europeans.
Additionally, in a world where WWI and WWII is avoided you'd likely have enough population surplus during the first decades so that Algeria, Tunisia and Libya today would be considered part of their respective homelands with a European majority population.
Another point to consider is that without WWI, colonialism would likely drag on. Europe could afford staying in its colonies and investing there much longer. That should lead to more immigration from there into Europe during and after the colonial era - Germany today could easily have 1 million descendants of former colonials that live in the country for generations.
Actually avoiding WWI should already do much. Prior to WWI, many European countries showed significant population growth and prosperity. If that had continued, you'd likely have a more conservative setting with higher population growth than IOTL plus millions of dead avoided plus the possible kids of those who died IOTL.
I'd also assume that a continuing "belle epoque" should preserve the traditional conservative elites much more than IOTL, leading to a more conservative Europe with higher population growth.
Then you should also avoid the Russian revolution. Without WWI, WWII, Stalin and the Soviet Union Russia alone could contribute 100 million additional Europeans.
Additionally, in a world where WWI and WWII is avoided you'd likely have enough population surplus during the first decades so that Algeria, Tunisia and Libya today would be considered part of their respective homelands with a European majority population.
Another point to consider is that without WWI, colonialism would likely drag on. Europe could afford staying in its colonies and investing there much longer. That should lead to more immigration from there into Europe during and after the colonial era - Germany today could easily have 1 million descendants of former colonials that live in the country for generations.