Simplify the following text for a Grade 10 native English-speaking person.
Original: He was soon elected captain of the Donnybrook company , then commandant of the Third Battalion and adjutant of the Dublin Brigade .
Simplified: After the outbreak of World War I in August 1914 , de Valera rose through the ranks and it was not long before he was elected captain of the Donnybrook company . Preparations were pushed ahead for an armed revolt , and he was made commandant of the Third Battalion and adjutant of the Dublin Brigade .