against police misconduct in the United States

has looked a lot like this,

shrouded in a thick cloud of tear gas.

[people shouting]

Some of the sounds in this video may be shocking.

[explosion]

And some of the footage may be disturbing.

[explosion]

- Back up!

Reporter: Police on the roof

are firing volley after volley of tear gas.

Nobody was doing anything.

Reporter: Step back, get back, get back, get back!

You're ahead, you're ahead.

Reporter: There is so much gas that has been launched again

that you can barely even see that line of officers.

[explosion]

Narrator: The use of tear gas has almost

become synonymous with the protests,

and it's nothing new.

[people screaming] [explosion]

On June 1, law-enforcement officers used a variety

of less-lethal weapons on peaceful protesters

outside the White House,

creating a scene eerily similar to one

from nearly a century ago.

In 1930, police used tear gas to disperse a group

of unemployed demonstrators in front of the White House.

Announcer: Washington became a battleground.

Narrator: Two years later,

President Herbert Hoover authorized the use of tear gas

on American veterans gathered in Washington

to demand their promised, yet unpaid bonuses.

Announcer: Using tear gas,

the troops methodically set about dispersing the marchers

in as bloodless a manner as possible.

Narrator: In the decades that followed,

law-enforcement agencies around the world

commonly dispersed large assemblies

of protesters with tear gas.

But tear gas was initially developed as a weapon of war.

So how did it become the weapon of choice

against protests?

Today, the business behind tear gas

is worth billions.

Announcer: Reliability and high performance

are our binding guarantee.

Narrator: Less-lethal weapons, as they're called,

are weapons intended to limit the escalation of conflict

without lethal force.

This industry was worth about $6.3 billion in 2016

and is projected to grow to $11.3 billion by 2023.

Tear gas represents about 25% of the industry,

meaning by 2023, it could be worth about $3 billion a year.

Anna Feigenbaum: This is completely a for-profit industry.

Narrator: This is Anna Feigenbaum,

the author of a book about the history of tear gas.

Feigenbaum: There is constantly

new innovation in this industry.

We're seeing pushes to put more and more

equipment into police hands.

[explosion]

Narrator: And the industry's rise is tied

to why it was originally developed.

The first known use of tear gas was in World War I,

when French soldiers fired tear gas grenades

into German trenches.

It was one of many chemical weapons used in the war,

during which over 90,000 soldiers died

from exposure to poisonous gases.

Announcer: A meeting of European foreign ministers

in Locarno, Switzerland.

Narrator: A 1925 treaty known as the Geneva Protocol

banned the use of "asphyxiating, poisonous

or other gases" in combat.

But the United States would not ratify the agreement

until 1975 and held the stance

that the protocol did not apply to nontoxic gases

or chemicals that could be used for riot control.

Other countries disagreed.

Jamil Dakwar: The idea was that if you allow tear gas

to be used in armed conflict situations,

there could be escalation of other chemical weapons

that would be increasingly dangerous

and would cause mass casualties.

Narrator: And the protocol also did not limit production

of those weapons, so production of tear gas grew.

[gas spraying]

Feigenbaum: The Chemical Warfare Service,

which had been doing a lot of this R&D,

wanted to continue.

And there was a big push to try

and validate its continued existence.

And one of the main drivers of that push

was a guy named Gen. Amos Fries.

He decided that tear gas could have a lot of uses

for security and for law enforcement.

And so he worked to create this kind of commercial

or domestic market in tear gas.

Announcer: The jumper repeater grenade

discharges three large blasts

of tear gas in rapid succession.

Narrator: Categorized as a less-lethal weapon,

tear gas is defined by the CDC as any chemical agents

that "temporarily make people unable to function

by causing irritation to the eyes, mouth,

throat, lungs, and skin."

Announcer: Six smoke-filled jumper repeater grenades

make an impressive display of saturation.

Narrator: Tear gas manufacturers

aggressively marketed their products

to law-enforcement agencies.

- How are you, Mr. Matthews? - Stick 'em up!

Narrator: Like in this promotional film from 1930

that illustrates how tear gas can be used

to thwart bank robbers.

- That's my last job.

Narrator: The marketing worked.

- Well, it's better than being shot.

Narrator: Tear gas became a weapon of choice

for police tasked with dispersing large crowds.

Announcer: With the army on the way,

the strike scene is hectic.

Narrator: In the early 20th century,

police often used tear gas during labor strikes.

Announcer: Then comes trouble, and police tear gas.

[explosion] [people shouting]

After the pin is pulled,

the grip on the strap handle controls the firing mechanism.

Narrator: Manufacturers weren't just selling

tear gas itself.

Announcer: When the handle is released in throwing,

the grenade is activated.

Narrator: They were also hawking must-have accessories.

Announcer: In a special kit available for immediate use

is a complete assortment of gas munitions,

including projectiles and grenades.

Narrator: And throughout the 20th century,

tear gas was used more frequently

on protesters around the world.

In Japan,

Germany,

Malaysia,

Vietnam.

Announcer: South to Saigon,

tear gas has been used to crush recent street rioting.

[explosion]

Narrator: Northern Ireland.

Announcer: Washington police used tear gas

to drive them away.

Narrator: Back in the US,

police continued to wield it on protesters.

Along with labor strikes, police used tear gas

at political and human rights protests,

like the 1965 Civil Rights protests in Selma, Alabama.

And in 1969, when police used tear gas

to disperse groups protesting the Vietnam War.

Feigenbaum: There was resistance and people saying,

"Well, how can you ban this in war but then allow it here?

How could we have said that these chemicals

have no place as part of military strategy,

and then you're using it on civilians?"

And so that strangeness or almost what seems

like an absurdity of that exceptional clause

has long been pointed out.

Narrator: But the United States always had exceptions

when it came to tear gas.

The country used tear gas and other chemicals

during the Vietnam War, both abroad and at home.

[explosion] [people shouting]

More limitations were put in place in 1993

with the Chemical Weapons Convention,

a treaty that explicitly banned agents

like tear gas "as a method of warfare."

[explosion]

But it still did not ban its usage in law enforcement,

including riot-control instances.