A merger between Astra of Sweden and Zeneca Group of the United Kingdom formed AstraZeneca in 1999. The firm sells branded drugs across a number of major therapeutic areas, including oncology (about 40% of total revenue), cardiovascular, renal, and metabolic (25%), rare disease (17%), and respiratory and immunology (15%). The majority of sales comes from international markets, with the United States representing close to one third of its sales.