。
Far too many people are indifferent to politics.
Literal
Too-excessively many people [subject-が] politics [to-に] indifferent be-[formal-である].
あまりにも is an intensified form of あまり, emphasizing excess — 'excessively, too much.' 無関心 is a な-adjective ('indifferent'); here it attaches with the formal copula ~である rather than ~だ, giving the sentence an essayistic tone. Note that 政治に — politics is marked with に, the particle for the object of mental attitudes (similar to 興味がある, 反対する).