Brutus' fears refer to the concerns expressed by the Anti-Federalist thinker in 'Brutus 1,' where he warned against the potential dangers of a strong central government established by the proposed Constitution. He feared that such a government would lead to the erosion of individual liberties, create a ruling elite, and ultimately threaten the sovereignty of the states and the rights of citizens. These anxieties highlighted the conflict between Federalist and Anti-Federalist perspectives regarding the balance of power in the new nation.