Canadians are currently learning tough lessons about national security thanks to United States President Donald Trump's repeated annexation threats.

It's clear that American proclamations of support for universal human rights, national sovereignty and a rules-based international order can vanish with a change of leadership. These ideals, though tarnished by some past U.S. actions, have now been replaced by the predatory dictum known as "might makes right."

Although it seems unthinkable that Trump will invade Canada, we live in an increasingly unstable world and Canadians need to be prepared for the worst. In the midst of a federal election campaign, party leaders need to present innovative ideas to fight Trump and potential American aggression.

Read more: An American military invasion of Canada? No longer unthinkable, but highly unlikely

Unfortunately, the common assumption is that national security depends wholly on military strength and alliances. But the emergency Canada is now facing demands a rethink.

Of course, Canada would not dispense with its military. It's needed, especially to defend Canada's northern frontier. However, Canada cannot match the U.S. in military power, nor would anything be achieved if it broke its commitments to the United Nations' Non-Proliferation Treaty - a pact designed to prevent the spread of nuclear weapons - by acquiring nukes.

Either of these tactics would be suicidal. Canada's real strength is its unity and institutions.

Canadians can paralyze military might through civil, non-violent resistance. Familiarity with these techniques could empower Canadian citizens to preserve a vibrant democracy.

Non-violent resistance can not only a more effective defence, but also much less devastating in terms of lives lost and property destroyed. Responding to an invasion with military force would only mean widespread casualties and the destruction of Canada's largest cities.

Canada should therefore aim to subvert the will of the occupying force, not drive it, through armed defence, to fear, hatred and further violence.

Non-violent resistance involves using a country's citizens and institutions to deter an invasion, and if that fails, to defeat and drive out the invaders. It has a long history both as a spiritual practice and a strategic weapon.

Civil defence, however, only emerged as a strategic concept in the 1980s and 1990s. It is a system of deterrence and defence that relies on a united and resolute citizenry employing only non-violent tactics.

An early American proponent was the Albert Einstein Institution's Gene Sharp, an American political scientist. Recent advocates from around the world - Srdja Popovic, Erica Chenoworth and Michael Beer - follow in Sharp's footsteps.

Civil defence is not merely a theory. There is a long history of improvised civilian resistance to invasions, most recently in Ukraine.

Ukrainians undertook many inspirational acts of non-violent resistance following the Russian invasion in 2022. They blocked tanks and convoys, berated or cajoled Russian soldiers to undermine their resolve, gave the wrong directions to Russian convoys, refused to co-operate and mounted spontaneous protests in occupied towns. But then the bloody carnage on both sides overwhelmed civilian defence.

Countries that include Sweden, Switzerland, Finland, Germany and Lithuania have institutionalized civil defence at various times. In Canada, civil defence was part of the mandate of Public Safety Canada during the Cold War. The idea then faded, being replaced by emergency management.

Public Safety Canada protected Canadians from both human-made and natural disasters. The agency, now the Department of Public Safety and Emergency Preparedness of Canada, should be resuscitated. The toll being exacted by climate disasters is reason enough.

Non-violent resistance involves determined citizens deterring an aggressor by signalling that the targeted country is united in opposition to a takeover.

A potential aggressor fears contagion from the democratic ethos of these citizens. If invaded, the civilians defeat the invaders by rendering their society ungovernable by the aggressor.

When the Warsaw Pact army invaded Czechoslovakia to crush the "Prague Spring" in 1968, the commanders soon learned that tanks and heavily armed soldiers were useless against unarmed civilians who refused to comply. The country was unruleable. Soviet troops were also infected with the democratic spirit and had to be rotated out of the country. It took several months and concessions from the Soviet Union before order could be restored.

The invader cannot consolidate control if citizens and their institutions refuse to comply with its rule. The tactics involve a complete refusal to co-operate with the occupying force along with open defiance.

That means that governments at all levels in the invaded nation continue to supply only basic services: clean water, electricity and policing, for example. Governments resign and civil servants find ways to subvert every order issued by the invader.

Crowds fill urban squares in silent or derisory defiance of orders, making it apparent to all - the occupiers, the dictator's audience back home, less committed citizens and global observers - who are the true purveyors of violence against non-violent people

Throughout the occupation, citizens and non-governmental organizations focus on subverting the loyalty and morale of the occupying troops and functionaries and rallying international support.

In Canada's case, the long history of friendship with Americans would likely mean that the morale of the occupiers would be low. The aim is to encourage defections by soldiers and functionaries, and erode the support base of the dictator. This erosion of support could lead to the overthrow of the leader, or at least to his concoction of a compromise to cover a retreat.

Attracting international support to Canada's cause would not be a challenge. Trump has already alienated most of humankind and foreign governments during his first weeks in office.

Non-violent resistance is most effective with nation-wide training, organization and leadership. The national government is best equipped to provide the facilities. Training of volunteers could include responding to natural disasters and emergencies, as well as implementing a civil defence strategy.

Yet partisan divides and apathy make such nationwide training difficult. It would likely be viewed with suspicion by right-wing populist forces in this era of conspiracy theories and misinformation.

Read more: How conspiracy theories polarize society and provoke violence

Apathy might also be a problem.

These considerations suggest that top-down, apolitical training in civilian defence may not work. If so, training and organization should be the goal of as many existing civil society associations as possible: churches, synagogues, temples, civil rights groups, unions, Indigenous rights organizations, peace advocates and climate groups, for example.

The manual authored by Michael Beer, the longtime director of the Nonviolence International non-governmental organization, includes more than 300 tactics. Widespread training and organization can not only deter aggression but ensure countries remain free of tyrants.

Amid the ongoing threats against Canadian sovereignty, Canada is an ideal candidate for effective civil defence. Although it might be unlikely Trump will order a military invasion of Canada, a united country capable of non-violent resistance decreases the risk.

Canada cannot match the U.S. in firepower or economic strength. But it shares with America a language, a history of common struggles, myriad cross-border personal relationships and basic democratic values still considered important by many Americans, if not Trump.

All of these factors give Canada considerable leverage.