Have been at the forefront of every important social change in the united states from the beginning of the nation.

Nonprofit organizations is the element that completes the phrase.

Have been at the forefront of every important social change in the united states from the beginning of the nation.

Explanation:

Nonprofit organizations are public-oriented groups that look to satisfy a certain population need in particular. Right now, there are around 1.5 Million non-profit organizations in the United States, including foundations, charitable organizations, chambers of comers, civil leagues, etc. The first knowledgeable nonprofit organization was The Peabody education fund which was founded in 1867, it's objective was to help poor white persons and ex-slaves to reach education to develop.

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