Which law /legislation protects the individual against human rights violation

There are multiple such laws, and each country has one, if not many. These laws can address general issues (the right to live) or very detailed issues that deal with specifics.

I will name only one example: Universal Declaration of Human Rights by the UN, which was signed by many countries.

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.