CAPE COAST, Ghana — President Obama traveled in his father’s often-troubled home continent on Saturday, where he symbolized a new political era but brought a message of tough love: American aid must be matched by Africa’s responsibility for its own problems. “We must start from the simple premise that Africa’s future is up to Africans,” Mr. Obama said in an address televised across the continent. For all its previous sins, he said, “the West is not responsible for the destruction of the Zimbabwean economy over the last decade, or wars in which children are enlisted as combatants.” “These things can...