Due to my above average performance in my Bachelor's, my university (which is the toppest one in my country) allowed me to enroll a master's course directly. This is really a great opportunity and is only given to 15% of the students. However I decided to drop out in the first semester and try applying for other universities abroad for the same degree and field of study, because my country has undergone serious conflicts and it is no longer safe for me to go out to my university. Should I explain the gap (which is 1 semester to 1 year) now? Is it completely viewed as a negative thing that I dropped out even though it was because of circumstances out of my control? Would it matter that I tell them I was eligible enough for the same course in my university or is it pointless?
Should I explain the gap (which is 1 semester to 1 year) now?
In general, you will be required to disclose your full academic history, including the fact that you enrolled as a master's student but did not finish your first semester. Given this, you certainly should explain the reason for your decision to leave.
Is it completely viewed as a negative thing that I dropped out even though it was because of circumstances out of my control?
It is not a negative so long as you explain it clearly. For example, if you say "I had concerns about my safety and decided to drop out" -- well, this is a little unconvincing, because I cannot judge whether your concerns were reasonable or not. On the other hand, if you say "I had to flee from Bakhmut University because the city was completely destroyed during the Russian invasion" -- this is very convincing, and does not reflect poorly on you at all.
Would it matter that I tell them I was eligible enough for the same course in my university or is it pointless?
You were admitted to the top university in your country; this is presumably impressive. The mechanics of how you achieved an offer of admission are not particularly important. You can mention it if it helps the narrative, but I do not expect it will make much difference.