I am curious in theories on "whether the history is destined or happened because a series of random events", discussions on "what if Hitler/George Washington/etc was never born, will the history be different?"
Do you have book recommendations for the casual enthusiast of history?
You should check out the Stanford Encyclopedia of Philosophy article on the subject. It will give you an article-length survey of the subject, along with excellent sources. The SEP is the premier tertiary source for philosophy (not just on the internet) and will help you with basically any issue in philosophy.
You can also ask at /r/askphilosophy for more recommendations.
What is History? by E H Carr is a good read for how history is written and perceived.
Georg Hegel's Phenomenology of Spirit is a landmark work in both the history of philosophy and the philosophy of history. In it he lays out an argument for the growth of human spirit, knowledge, consciousness, etc in the larger narrative of world history. Hegelian philosophy, most notably the concept of historicism, would go on to influence many continental schools of thought and other famous thinkers such as Nietzche and Marx.
It's not exactly light reading, but Hegel's works do shed some light on whether history is something that can be seen as deterministic or goal-oriented versus chaotic or random.
As for sources, my main one would be... Hegel's Phenomenology of Spirit. Here is probably the best basic summary of it I could find.