Japan's Prime Minister has formally announced his resignation, paving the way for the country's sixth leader in 5 years. His move follows nationwide criticism of his response to the devastating earthquake and tsunami that took place in March, and triggered a nuclear crisis at the Fukushima plant. The twin natural disasters claimed the lives of more than 15,000 people, with survivors complaining about slow recovery efforts. A new leader of the ruling Democratic Party, who'll most likely become Japan's next Prime Minister, will be chosen on Monday.