“The truths of the Declaration of Independence are not limited by time or place,” John Quincy Adams wrote in 1839. “They belong to the nature of man in every age and every clime. They may be subdued, but they can never be suppressed. They are truths at Constantinople and Pekin, at London and Paris, at Charleston and at Philadelphia.”

To Adams, the document showed that America was an idea and an ideology as much as it was a place.

The original writers of the declaration intended to produce a document to reassure Americans of the justness of their cause, and to appeal to potential supporters abroad. But over time, the Declaration of Independence took on a much greater meaning. It was used as an announcement of a new nation’s founding, as a diplomatic appeal for recognition, as a statement of political philosophy and as a call to defend liberty at home and abroad.

Today, as American democracy comes under pressure at home and from hostile actors abroad, the declaration is as relevant as ever. Not because our times mirror those of 1776 but because they are another step in the continuing evolution of the declaration’s meaning, both within the United States and across the world.

One of the original purposes of the declaration was to persuade the 13 colonies about the perilous and necessary undertaking they were about to embark upon, and to affirm what their political revolution was for and what it was against. It was also intended as an international declaration: a diplomatic statement that the citizens of the newly independent United States were not mere rebels, but sovereign actors who had legal claims to independence, diplomatic recognition and material support.

Over the years, however, the declaration took on new meanings. According to the historian Pauline Maier, the document was almost completely forgotten by the new American government. But it was later revived by Jefferson’s supporters as a means to justify an alternative political vision, and was subsequently “elevated into something akin to holy writ, which made it a prize worth capturing on behalf of one cause after another”. And, in Abraham Lincoln’s potent hands it “became not a justification of revolution, but a moral standard by which the day-to-day policies and practices of the nation could be judged”.

While it might have been written at a particular moment, its expansive language meant that over time, other groups and people would reinterpret the declaration’s demands for equality, liberty and “unalienable rights”. At the Seneca Falls Convention of 1848, women inserted themselves into this self-evident truth with the claim that “all men and women are created equal”. A few years later, one of their supporters, abolitionist Frederick Douglass, transformed the words of the declaration into a call for racial justice and emancipation. He sought not to reject “the great principles it contains” or “the genius of American Institutions”, but rather recognised that it was the very transferability of the declaration’s principles to contemporary circumstances that gave it its power.

But if theirs were calls for the rights inherent to all Americans, there were others who saw the value of the declaration abroad as well. Hence John Quincy Adams’s belief that the declaration’s message would one day have resonance in Istanbul and Beijing like it did in Charleston or Philadelphia. Delivering his famous July Fourth address of 1821, Adams, then serving as secretary of state, proclaimed that the central message of the declaration was “the successful resistance of a people against oppression, the downfall of the tyrant and tyranny itself”. For Adams, and for many subsequent Americans, this was America’s mission, and it had universal application.

Shortly before the First World War broke out in 1914, Woodrow Wilson reflected on the declaration’s meaning for a nation well over a century after its writing. He called on a crowd in Philadelphia to breathe new life into the document, to find ways to translate its lofty ideals into real-world policies. Four years later, having taken America into a war to make the world safe for democracy, he expanded his call, arguing that “it is our inestimable privilege to concert with men out of every nation what shall make not only the liberties of America secure but the liberties of every other people as well”.

If the notion of bringing the promises of the declaration to the world was not new, the rise of Imperial Japan and Nazi Germany transformed the declaration yet again. As the storm clouds gathered before a second, and even more violent, world war, Franklin Roosevelt on July 4, 1941, noted “in the past few years, a new resistance, in the form of several new practices of tyranny, has been making such headway that the fundamentals of 1776 are being struck down abroad, and definitely they are threatened here”.

No longer was it sufficient to simply promote freedom at home or link arms with other nations to restore the peace, as the United States had done in 1918. To Roosevelt and his successors, the rise of these new ideologically committed and powerful tyrannies demanded that the declaration’s cause become one of proactively responding to threats, harnessing the collective powers of the free world and leading the fight against dictatorship abroad.

In the early years of the Cold War, after North Korea shattered the rough peace by invading South Korea, Harry Truman updated the declaration for the new leadership role the nation was assuming. Broadcasting from the Washington Monument on July 4, 1951, he warned that “freedom must be fought for today, just as our fathers had to fight for freedom when the Nation was born” because freedom was under attack on a worldwide basis. It was an attack, Truman declared, that must be met: “If we with all that we have in our favour do not succeed, no other free government can survive — anywhere in the world — and the whole great experiment that began in 1776 will be over and done with.”

Truman also believed that fulfilling the “whole great experiment” required seeing America’s domestic and international efforts as two sides of the same coin. “It is for this reason,” Truman declared, “that persecution of minorities, which is wrong anywhere, is worse in America.” This meant that the nation’s legitimacy as a sovereign nation would always be judged against the promise of its ideals and measured next to its commitment to extending those rights to others. And if the country ensured those rights at home, America could be a model to the world as it lent a helping hand to those struggling against oppression anywhere.

The declaration was written to justify the independence of the early American republic. But its message of unalienable rights, equality and liberty have echoed through time and across borders. As the historian David Armitage has observed, the declaration served as the model for some 193 other nations including Haiti in 1804, New Zealand in 1835, Vietnam in 1945, Israel in 1948 and, more recently, Kosovo in 2008. This message speaks to men and women seeking freedom from oppressive governments. The resonance of the Declaration of Independence may be in its universality, but its power derives from its ability to speak to changing circumstances and, as Fredrick Douglas declared, its demand to “make it useful to the present and to the future.”

The Fourth of July offers an opportunity to reflect on America’s birth, history and mission. It also serves as a reminder that America’s influence derives from the power of our example, that America’s motivating ideology has always been resistance to tyranny, and that the American Revolution was a moral statement embodied in the Declaration of Independence: equality for all under the law, a government subordinate to the people and a commitment to promoting liberty at home and abroad.

• Charles Edel is a senior fellow at the United States Studies Centre at the University of Sydney, and previously served on the US Secretary of State’s policy planning staff