Is loneliness innate or caused by external conditions?

Loneliness is neither innate nor it is caused by external conditions.

Rather I would term it as an internal phenomenon acquired over a period of time, it's not natural in any way. Nature doesn't teach us to be alone, everything in nature runs in harmony, and all of them have respective responsibilities and importance in the process. The feeling of loneliness arises when you detach yourself with the outer world for various reasons, but remember, all of them are your own, self-created. Expecting too much from yourself or accessing too inferior to others also causes loneliness. Whatsoever may be the cause? it's from inside. Start asking, start demanding and all external forces will be with you as never before.

This topic is endless, I am but briefly answering your question.