When did the first heroes of olympus book come out?

The Lost Hero came out on October 12, 2010

answer; i believe that the correct answer is (chronological order);

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.