What are the most effective tools for establishing and preserving freedom?

There could be a number of answers to your question, as it is the sort of question calling for an essay in which you state a thesis and defend it. 

A possible thesis would be that the most effective tools for establishing and preserving freedom are effective legislatures and a fair and strongly functioning system of courts. 

Without effective legislatures (on the state and national level), laws and governance bog down and the rights and freedoms of citizens can be eroded by special interests or powerful individuals and groups. Without courts functioning fairly and firmly to uphold laws that protect citizens' civil rights and liberties, the freedom of all citizens can be compromised by those who have greater advantages of wealth or position. 

For another possible thesis, I would. point you to thoughts from Alexis de Tocqueville's famous work from the 1830s, Democracy in America. Tocqueville put great stress upon the direct involvement of all citizens in the democratic functioning of society, through things like service on juries in the court system and by their regular association with one another in civic groups. Tocqueville urged that in a democracy, individual citizens need to learn to unite in association with one another to work as a group to protect their freedoms against the encroachment of tyranny. Tocqueville said that the most democratic country on earth is, above all, where individuals have "most perfected the art of pursuing the object of their common desires in common." He thought there is a "necessary relation between associations and equality."

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explanation:

they made rome the dominant power in the mediterranean.