The Harmonium hails from Germany and it is not an Indian instrument. Also, it is a equal tempered instrument. But the harmonium is a very common accompanying instrument in Hidustani Classical and Bhajan.
Whilst the harmonium is not used for South Indian Carnatic Music, violin is commonly used. The violin was also adopted from western world.
Why did Hindustani music pick harmonium and Carnatic Music pick violin? Why did we adopt Western instruments even though we have a lot of Indian instruments?