Some books, old as they might be, tend to leave some significant marks within us.
In my case, the most significant writer that had the biggest impact, was Emilio Salgari. Albeit he never left Italy, he managed to describe places around the world with such vivid detail that the reader actually felt there. One of my favourite series was about the Indian prince Sandokan, who fought viciously against the British in order to reclaim his empire stolen by them.
What caught my attention was the fact that there were no good guys or bad guys in these books. Albeit Sandokan was the hero we cheered for, he was capable of tremendous atrocities, like killing every single person on a ship he may had captured. At the same time, the bad guys, in this case the British forces, were not just bent on the destruction of everything they came across. We got a sense that these were real people doing what they did because they seriously believed in it and not because they had some secret agenda of evil they needed to follow.
The most impressive thing is that there was a real sense of comradeship in these stories, combined with admiration and respect between adversaries. Field Marshall Rommell and General Patton were enemies, but they had profound respect and admiration for each other and what each had achieved strategically. This type of chivalry, in our present-day world, seems to have disappeared, replaced instead with this weird and ever-changing sense of "respect" based on who packs the biggest gun or the most bling-bling.
On top of that, in these books, I learned about life: good people die, bad guys win. Bad guys would do good things and sometimes the good guys, especially when pushed to their limits, would do horrible things. I seem to have the habit, every once in a while, to grab one of the twelve books and devour it in a day. As a kid, it used to take me weeks to read one of them.