The U.S. Department of State has issued four "Do Not Travel" warnings in the past two weeks. The warnings are based on factors including crime, terrorism, health concerns, and natural disasters.

In April, Travel + Leisure reported Royal Caribbean would change its cruise routes to avoid a port stop in Labadee, the company's private beach resort on the northern coast of Haiti.

Can you guess which iconic cruise line has been sailing the longest? Check out the most historic cruise operators remaining ...