As you write your 200-word essay, you will find many resources discussing the subject; I've pasted below links to two articles from 2013, as your assignment specifies that you should be looking at issues confronting Starbucks in 2012.
The first set of issues confronting Starbucks is inputs. Many of the many coffee growing areas are in regions of political or economic instability. Maintaining reliable sources of premium coffees despite this is a perennial issue for Starbucks management. A related issue is the possibility of spikes in coffee price or of long term increases.
The next issue management should worry about is competition, both on the high end from the increasing number of artisan coffee shops and on the low end as fast food restaurants offer better coffees and a wider range of coffee drinks. Regional chains such as Seattle's Best and Caribou Coffee are also challenging Starbucks in some markets.
Finally, retaining quality staff is an increasingly important challenge as Starbucks expands, one it part that it is addressing by such radical innovations as its partnership with Arizona State University.