THE last Detroit Daily Post, July 16, 1870, announces that France has formally declared war against Prussia. All Europe is in intense excitement. The reasons for thus hurling millions of men into mortal combat, are set forth as follows: 1. The insult offered at Ems to the French Count Benedetti. 2. The refusal of the King of Prussia to compel the withdrawal of Prince Leopold's name as a candidate for the Spanish throne, and 3. The fact that the King persisted in giving the Prince liberty to accept the crown. These causes the British Cabinet consider unworthy even of discussion. July 15, Queen Victoria made a final appeal for peace to both the kings of France and Prussia. The sympathy of the powers of Europe is against France in this precipitate and causeless war. It is considered by those who best understand the situation, that Napoleon stakes his empire on this move, with much greater chances for failure than for success. All Europe will probably be involved.