There are three ways to separate a run-on sentence: use a semicolon, use a comma and a conjunction, or put a period and capitalize the first letter in the next word. In this case, we have to do the final option, because we have to make two separate sentences; the other options will make a compound sentence.
1. Queen Elizabeth I knighted Raleigh, and he was appointed captain of the Queen's guard. He later set sail on an unsuccessful search of El Dorado, the legendary city of gold.
In this case, we put a period after 'guard' and capitalize the 'h' in 'he' because that is the point where the sentence can be separated into two complete sentences.
2. Queen Elizabeth liked Raleigh, however, her successor, King James I, did not. In 1603, he was accused of plotting against the king and sentenced to death, but only served 12 years.
We separate this sentence between 'not' and 'in' for the same reasons that we separated the first. That is the part of the sentence where it can be separated into two sentences that function on their own.
Hope this helps!
