Which amendment to the constitution gave the national government the power to prevent state violating the rights of their citizens?

The correct answer is the 14th amendment.

The 14th amendment was passed in 1868 and was a critical part of Reconstruction. This amendment stated that anyone born on American soil would be considered a citizen. Along with this, the 14th amendment also contained the Equal protection clause. This amendment states that no state can deny "the equal protection of the law" within their jurisdiction (aka territory). This amendment ensures that states cannot take away a citizens constitutional rights.

Getting elected because not many people were voting