What does the 11th Amendment bar in terms of lawsuits?

The 11th Amendment to the United States Constitution primarily establishes that individuals cannot sue states in federal court without the state's consent. This amendment was adopted in response to concerns that states should not be subject to lawsuits from private citizens in a federal forum. It protects the states' sovereign immunity, meaning that states cannot be sued for money damages or injunctive relief in federal court by private citizens or citizens of another state.

While the 11th Amendment does not prevent suits brought by the federal government against states or lawsuits where a state consents to be sued, its main function is to shield states from private litigation initiated by individuals. This is why the correct answer refers to private citizens suing states, which is barred under the 11th Amendment.

The other options address different legal principles that do not directly involve the protections offered by the 11th Amendment. For example, lawsuits against the federal government are governed by different statutes and legal doctrines. Similarly, individuals suing each other or states suing other states involve different legal considerations outside the scope of the 11th Amendment's sovereign immunity provisions. Thus, the clarity of the 11th Amendment lies in its specific application to the relationship between private citizens and states in the context of federal jurisdiction.