Most people wouldn't pick a fight with someone twice their size.
The same goes for countries.
But while we can judge a potential opponent by their height
and weight, countries' leaders, in theory, consider the balance of power.
It's a measurement of the relative strength between countries,
comparing their military's resources, wealth and population,
as well as their relationships with other countries.
When that relative strength is more even or balanced,
those countries are less likely to fight each other.
Because the expected benefits of war would likely be smaller than the costs.
But when that relative strength is less even or imbalanced,
the stronger of the countries might be tempted to attack the other,
because the stronger one might expect the benefits are more to outweigh the costs.
However, imbalanced countries can avoid war
and well-balanced countries still fight wars
because there are many other factors that determine whether countries act
aggressively towards each other.
The First World War provides one of history's
most enduring examples of this idea when the fairly even balances
of power between countries in Europe at the beginning of the 20th century,
weren't enough to prevent conflict from breaking out.
Before World War I in the 1800s,
there was a decades long era of relative peace in Europe,
when the major countries maintained rough balances of power among themselves.
And while they occasionally fought with each other,
they typically avoided massive wars
over one another's principal territories.
It extended into the early 1900s
when the rough balances of power were largely maintained,
as Britain and Germany became the strongest countries in Europe.
Both had large populations and economies, robust
militaries and strategic partnerships with other countries.
Germany formed an alliance with Italy and Austria-Hungary.
All three agreed that if a member were attacked by certain countries,
each would help the other attacked country in various ways.
These defensive partnerships increase the members strength
relative to countries outside the alliance.
But Britain, France and Russia established a similar partnership,
and power remained roughly balance between the two groups.
For each of these six countries, the costs of starting a war
far outweighed the potential benefits.
However, in 1914,
leaders miscalculated those costs and benefits
as they responded to a political assassination,
recklessly escalating the situation in Europe
until they dragged their alliance networks and many countries
across the world into a brutal, costly war
for four long years that settled little
and in which the costs far exceeded any benefits.
While a balance of power isn't enough to stop countries from fighting.
An imbalance can certainly encourage aggression,
as was seen in the lead up to the Second World War.
After World War I,
the victors, Britain, France and the United States,
all exhausted by war, reduced the size of their militaries
and placed limits on the warships they could build.
The victors, wartime enemies had been defeated.
But by the early 1930s, the military balance began to disappear,
as Germany, in particular, increased its military might.
British and French leaders called on Germany to stop,
but wouldn't back up any of their complaints with force.
This undermined the credibility of their threats and promises,
and further undermined the balance of power.
The new imbalances encouraged Germany to act aggressively.
Germany's leader, Adolf Hitler, repeatedly violated
the terms of the peace treaty from the end of the First World War
by openly rebuilding the country's military
and expanding German territorial control into neighboring countries.
If Britain and France had worked to maintain the balances of power,
they might have checked Hitler's
aggression with credible threats of military retaliation.
Instead, they accepted Hitler's demands with the hope
that if Germany was satisfied, it would remain peaceful.
This approach is referred to as appeasement, and it signaled to Hitler
that Britain and France had no political will to defend their partners,
further eroding their credibility
and encouraging Hitler to continue his campaign of aggression.
British and
French leaders belatedly realized their error
and started making more of an effort to counter Germany
by signing on to a defense agreement with neighboring Poland.
But it was too late to significantly alter the imbalance.
In 1939, Hitler continued his German expansion by invading Poland.
At which point Britain and France declared war on Germany,
marking the start of World War II, the deadliest
conflict in human history.
Imbalances of power can encourage aggression and balances
can encourage peace.
Ultimately, though, it's up to countries leaders
to accurately assess the balance of power that exist
and to do what is necessary to maintain them when they miscalculate
or fail to maintain military balances or underestimate the costs of war,
the consequences can be devastating.