Answer:
He was refused because of his bad health. He was about to participate in the Balkan Wars. He even went through preparation and everything, but still didn't participate in the war.
Step-by-step explanation:
Although the name Gavrilo Princip is mostly connected with the assassination of Archduke Franz Ferdinand he was involved in certain political processes even before. In 1912 he moved to Serbia and volunteered to participate in war, but as we already mentioned he was refused because of bad health.