The correct answer is option 1: United Nations Peacekeepers. Blue Helmets are a widely recognized symbol for the United Nations peacekeeping operations. When deployed, these blue-helmeted troops work in areas of conflict or post-conflict to maintain peace and security, protect civilians, and support the restoration of law and order. They are part of an international effort to prevent and resolve conflicts and promote stability in countries or regions experiencing violence or instability.

Option 2, Violent Non-State Actors, refers to armed groups or organizations that are not affiliated with any official government. These actors use violence to achieve their goals, often operating outside the framework of international law.

Option 3, Civil Society Organizations, refers to non-governmental organizations that work to promote social change, advocate for human rights, and provide services to communities.

Option 4, Environmental Organizations, refers to non-profit organizations that focus on advocating for and protecting the environment. They work towards environmental conservation, researching and addressing environmental issues, and raising awareness about sustainable practices.

Therefore, the United Nations peacekeepers are the correct definition for Blue Helmets.