Learn Russian: Руководство не доверяло президенту с 2011 до 2015 года. - The leadership did not trust the president from 2011 to 2015.

Because they follow the prepositions с (from) and до (until/to), both years must be in the genitive case. In Russian years, only the final word changes its ending. So you would say с две тысячи одиннадцатого до две тысячи пятнадцатого.

Why is the word for year (года) only written at the very end?

When expressing a span of years, you only need to use the word года after the final year. You could technically say с 2011 года до 2015 года, but dropping the first one sounds much more natural and avoids repetition.

Why is the president (президенту) in the dative case here instead of the accusative?

The verb доверять (to trust) always requires its object to be in the dative case. You can think of it as 'giving trust TO the president', which helps remember why it takes the dative.

Why does the verb доверяло have the neuter past tense ending -о?

Verbs in the past tense must match the gender of their subject. The subject here is руководство (leadership). Even though a leadership team consists of people, the word itself is grammatically neuter, so the verb takes the neuter ending -о.