The branch of government that has been most responsible for the incorporation of the Bill of Rights is the judicial branch. The judicial branch, since the early 1900s, has gradually been incorporating the Bill of Rights protections and saying that they apply to state actions as well as to actions of the national government. This process hase been called selective incorporation.
The Court has used the 14th Amendment to say that the states must follow the Bill of Rights. It has said that rights given by the Bill of Rights are part of the "liberty" that may not (under the 14th Amendment) be taken away by the state without due process of law.
The judicial branch is the branch of government that mainly is responsible for the incorporation of the Bill of Rights. Since most issues regarding the Bill of Rights involve individual freedoms, it is the courts that usually determine if these rights have or have not been violated.
There have been many court cases involving our freedoms protected by the Bill of Rights. For example, there have been cases involving freedom of speech. In the case of Schenck v the United States, the Supreme Court ruled it was legal for the government to pass laws limiting our freedom of speech if the words used presented a danger or threat. For example, it is illegal to yell the word “Fire” in a movie theater as this could cause a panic where people could be hurt or killed. Other Supreme Court cases ensured that juries didn’t exclude people because of race or sex. The judicial branch has been mainly responsible for enforcing the incorporation of the Bill of Rights.
The Judiciary or the Judicial Branch of the US government has been primarily responsible for incorporating the Bill of Rights. Originally, the Bill of Rights was applicable only to the Federal government. American Courts have been incorporating portions of it to the States and local governments and now the Bill of Rights is applicable to these governments as well. The US Supreme Court, in 1833, clarified that the Bill of Rights is only applicable to the federal government. However, beginning in 1920, a number of Supreme Court decisions interpreted the Fourteenth Amendment to include states as well, meaning that now portions of the Bill of Rights are enforceable against state governments. The Fourteenth Amendment provides for citizenship rights, due process, equal protection, immunity, etc. and has not only been applied to states, but for ending racial discrimination as well.