Both, nationalism and Islamism, were ways that were used by the authorities of the newly formed countries for unification and strengthening the position of the nation, and the politicians as well.
Nationalism was based on ethnic level, and it was a way of creating despise, revolt, anger, towards the other nations. It was used as a unification method and for creating a nationalist core, and in this way the authorities were able to create a large mass of people that were willing to fight for their own nation, and had a deep hatred towards the other nations.
Islamism was based on religious level, and it was promoting unification on religious basis, but was also creating lots of hatred and aggression towards other religions. In this way, the authorities were trying to create a strong religious core in the country, but also brotherly alliances with the countries that practice the same religion.
Both, nationalism and Islamism were terrible towards the minorities, and the nationalist were killing and committing genocides on ethnic level, while the Islamist were doing the same but on religious level.