What are the major factors that contributed to Xiaomi becoming a leading smartphone company in China?

What are the major factors that contributed to Xiaomi becoming a leading smartphone company in China? What capabilities would Xiaomi need to develop to compete head-to-head with industry giants Apple and Samsung? Xiaomi has been very successful in China, but how will they fare in the global market? What obstacles are they likely to face? What capabilities will they need to develop to expand globally?