The taxes were aimed at paing back the debt issued during the seven years' war.
Between 1756 and 1763 Great Britain fought against France because of the competition in the fur trade. Despite their victory, the Britons were sunk into debt.
King George III decided to have the colonists pay taxes despite their having no representation in the British Parliament in those days. Moreover in 1763 he issued a proclamation forbiding the colonists to settle beyond the Appalachians.
The debts issued by the Bank of England was the main cause explaining why so many taxes (Tea Act, Stamp, Townshend Act) were passed.