What did black codes achieve

Assuming you mean the Black Codes established in the United States during the mid-1860s, these codes sought to restrict the freedom of African Americans after the end of the Civil War. Because slavery was no longer legal, former slave owners and others still wanted to hold power over the free African Americans. They sought this power by forcing them to receive low wages in a labor economy or go into debt. Those who held power wanted to ensure that African Americans were not as free as others, and that they still had to work and owe society their labor and money. This unfortunately perpetuated the unfair treatment that African Americans faced after the Civil War.