What is the fine-grained topic of the following text: Yumbis Attack Event Summary: On Thursday 21st of May 2015, 1800-hrs EAT, approximately 40 militia men from Somali based Islamist group Harakat al-Shabaab al-Mujahideen entered a Kenyan Village known as Yumbis in Fafi area of Garissa County. Only return the topic.
Harakat al-Shabaab al-Mujahideen's attack on Yumbis village in Kenya