It has been called the "third army". Disease, that is. And when it becomes global in scale, it adds to the madness and destruction of wartime by ravaging military forces, decimating civilian populations, and confounding and sometimes even killing leaders.

The most dangerous part of this invisible contingent is its indiscriminate nature - it kills without regard and takes no sides.

The coronavirus, for its already extensive international reach, has been and will continue to intervene in many of the ongoing armed conflicts and destabilised regions around the world - from Afghanistan to Syria, to the protracted struggles between the Mexican government and that nation's various drug cartels.

Can we glean any lessons from history about what happens in wars when pandemics strike?

We know that no one is safe, not even politicians and generals.

During the outbreak of what some believe was Typhus, a plague that swept through Athens during the Peloponnesian War back in the fifth century BC killed Pericles, the famed general and statesman.

The disease did not stop there. It would go on to kill one-third of the population of Athens and demoralise the city-state's people. Overall, it would tilt the balance of power in the war towards Sparta, which went on to defeat Athens years later.

When people think about pandemics and war, it is most likely the case of influenza that swept the globe during World War I that comes to mind.

Influenza, or the H1N1 virus which reappeared as a new strain during the 2009 swine flu pandemic, was labelled the "Spanish flu" at the time of World War I - the reason being that of all the countries that were hit, Spain was the first to actually report on the illness due to war-time censorship elsewhere.

Regardless of its name, this pandemic wiped out armies, civilians and leaders alike. US President Woodrow Wilson, according to some, contracted the illness. When it came to the armistice of 1918, the president made little attempt to negotiate for US interests principally because of his 103 degrees Fahrenheit (39.4 degrees Celsius) fever and debilitated physical state.

Influenza also hastened World War I to its end. The US military machine was essentially paralysed as soldiers required care and fell victim to the illness in greater numbers than they did in actual combat.

The virus was particularly effective in halting the US's largest campaign of the war - the Meuse-Argonne Offensive along the Western Front from September to November of 2018.

Yet, the pandemic's real destruction came after, as it would infect more than 500 million people worldwide and claim more than 50 million lives.

In some conflicts, outbreaks have ended wars, but in others, they have prolonged them.

For instance, some believe that the US Civil War, which ran from 1861 to 1865, was extended by two years due to the spread of infectious disease.

That time, it was malaria that showed no allegiance and took no prisoners, taking aim at everyone that crossed its path.

In particular, the numerically and technologically superior Northern forces of the Union army ran into significant difficulties with the disease when it entered the hot and humid south. Malaria turned out to be just as formidable a foe to the southern Confederates as they were, in turn, decimated by the illness after the Union Force's naval blockade cut the supply of anti-malarial medication.

Right now, with so many conflicts raging around the world in so many different places, we are already seeing how the coronavirus is affecting military forces and armed struggles.

The war in Yemen, for instance, has apparently entered a ceasefire due to concerns over the spread of COVID-19.

Meanwhile, in Mexico, cartels are running short on necessary Chinese imports to produce methamphetamine and fentanyl - the latter substance being necessary for the production of heroin. The virus has slowed trade around the world, and international drug trafficking is no exception.

While this has led to a price rise for drug users in the US, it could also portend more violence in a country that has already been torn by years of conflict between different cartels.

Think about it: will groups engage in conflict with one another over scarce resources? If so, then will we see even greater numbers of internally displaced people in a country where thousands have been uprooted over the many decades of the drug war?

Similarly, Syrians with the virus face significant challenges after years of civil war have depleted the country's infrastructure. Syrian refugees could also bring a second wave of the pandemic into an already devastated Europe.

And what of our leaders? Some have already been infected, such as British Prime Minister Boris Johnson. But what about those engaged in the ongoing struggle in Afghanistan? What could happen to peace talks there, especially if some of the key individuals who are involved fall ill?

Does history provide illumination at times like these, especially concerning the impact of pandemics on war? If anything, it shows that the chaos and uncertainty that already resides in warfare is only compounded with diseases that have neither nationality, nor loyalty.

Not even leaders are immune.

Pandemics only raise the stakes, for everyone, in times of war.

It is hard to find hope during times like this, as diseases such as the coronavirus bring us all to recognise their power. Yet, if there is any, perhaps it is in forcing leaders and the rest of us to ask, is the violence ever really worth it?

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial stance.