I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "When the Emancipation Proclamation was announced, Tennessee was mostly held by Union forces. Thus, Tennessee was not among the states enumerated in the Proclamation, and the Proclamation did not free any slaves there. Nonetheless, enslaved African Americans escaped to Union lines to gain freedom without waiting for official action. Old and young, men, women and children camped near Union troops. Thousands of former slaves ended up fighting on the Union side, nearly 200,000 in total across the South."? 

Shiloh began when the __ launched a surprise attack.