Two of the issues that made it difficult for explorers during Columbus's time to explore unknown territory by sea were; inaccuracies of navigational tools made exploration by sea inconsistent and unpredictable and explorers had limited knowledge of the world’s geography.
Further Explanation:
During Columbus's time of exploring the sea was the best way to travel. The governments wanted to explore so they could use the sea for trade routes and commercial operations.
In addition to the answers above, other things that made exploration difficult during this time were;
early technology used was imprecise such as "dead reckoning"
the seas were challenging and inconsistent since they were uncharted
navigators could become lost
the financial risks were too high if the navigators and ships were lost
When Christopher Columbus did find America it was not intentional, he was actually going to Spain but he did not have the tool or the knowledge to get there and ended up going the wrong direction.
This was known as the "iron curtain." It was a term used to describe the boundary in Europe, which formed at the end of WWII and lasted until the ending of the Cold War.
