and a increasing number
...
an increasingHowever, whether it is necessary to travel abroad to experience their cultures has arisen as a controversial issue.
you are narrowing down the scope of your prompt which says -
learn about other countries
... culture is just one aspect of a country. There are more things other than culture that tourists are interested in. For example, natural beauty, wild life, landscapes, beaches, cuisine etc. So, introduce your prompt in its original sense.
Facilitated by modern world transportation, traveling around the globe within hours has become realistic. This means that everyone is now able to spend his/her holidays in the other side of the world if he/she wants so. In short, people can go anytime nowadays, which makes traveling quite a direct and easy way to understand foreign worlds.
You also need to include examples in your body paragraphs. It is a must feature for this task.