Secularism became the most necessary principle after 18th century in Europe. US was established in secular system in 18th century. Those countries became the most powerful countries in the world. When nationalism and secularism were united, the power of church got less on the societies. Ottoman Empire had also affected from this political system. Ottoman Empire became state. First of all, Balkan region was divided into new countries. Then the Middle East and North African regions were gone. Russian Empire collapsed in 1917 because of this system.
Mustafa Kemal grew up in Thessalonica (today’s Greek city), So he experienced this political system exactly. He realized that new modern states had been based on this principle. It means the separation of religious works and state works. So, the religious pressure will lose the impact on society. The development path will be opened for the society. Religion is between the God and the individual. Official state works have different specialty. Mixture of those terms causes some unfair benefits. This also harms the society. That’s why, Atatürk wanted to protect Turkish nation from this harm.
Always Atatürk.