How has religion changed between the years 1900 and 2000?

This is a great question. Since we are dealing with a hundred years, it is possible to address may elements of change. So, I will mention one of the greatest changes that has taken place.

It is safe to say that Christianity is the largest religion in the world (2.1 billion). So, when we speak of demographic change within Christianity, then we are talking about large scale changes. In view of this, we can say that Christianity has sifted in the last hundred years. What was once a very European religion is now no longer. Let me offer some facts.

There are more Presbyterian churches in South Korea that in Scotland, where Presbyterianism was started. China, once a closed country to Christianity, has more Christians than Germany, France and England combined. There is also an explosion in Protestant Christianity in Brazil and nations in Africa.  Brazil alone has over fifty million Protestant believers. Even in America, the greatest growth in churches can be seen in immigrant churches.  In view of these points, one of the great changes from 1900 to 2000 is the change in Christian population.

The church has moved from the West to the East and South. For more information, take a look at Philip Jenkins, a scholar of modern religion; he has written extensively on this topic with excellent scholarship.

How has religion changed from the 1900's to now?

There are many things that can be said. So, let me give you a few perspectives. 

First, since the 1900, fundamentalism in some of the major religions of the world has grown. Not only this, but these fundamentalists have at times become more radicalized. For example, think of the Muslim extremist in our world and what this has caused.

Second, contrary to popular beliefs, religion is growing in our world, even with the advancement of technology and science. This is one of the facts that has surprised many scholars. 

Finally, with the advancements that have taken place in our world, religion had to adapt and take stances on issues that are current, such as the human genome project.