How would you write an introduction about: Compare and contrast various ways that artists have been influenced by other cultures.
To effectively introduce a topic like this, it is very important to have particular examples in mind. You could certainly use your first sentence or two to introduce the topic on a broader level, but you will need to find a way to narrow your discussion to specific "ways." The best way to do this is to determine what examples you are going to marshal to your defense in your paper. Once you have selected your examples, determine what they have in common - remember to think about them broadly; your examples may not be very closely related, so thinking more broadly should help you think more laterally.
Once you have determined the basis for comparison - the ways artists have been influenced - determine to what effect the "ways" exert that influence. In other words, if you suggest that an artist was influenced by a certain culture in a certain way, what makes you think that is the case? Again, with this, you need to remember to think broadly for your introduction. For example, you could argue that by looking at specific works of particular artists, this is how an artist has been influenced by a specific culture.
It should be safe to make the assumption that all artists are shaped to some extent by the cultures with which they come into contact. For this reason, do not worry too much about whether your examples seem too narrow - though it is good to try to get an array of possible examples to strengthen those points you make.