Protesters are determined to block a new law that would allow extraditions to mainland China.

Police confronted them with tear gas and rubber bullets.

Beijing is not happy with what’s going on, very frustrated.

All flights in and out of Hong Kong have been cancelled as protesters occupied the airport.

There are growing fears that the Chinese government may use the military to crackdown on protesters in Hong Kong.

I think the movement has been able to maintain a high level of support

because the perception has been that most of the violence has been used against the unarmed protesters.

That's just caused a lot of outrage amongst Hongkongers.

We examined close to 330 major violent and nonviolent campaigns from 1900 to 2006.

And these were major campaigns that were challenging incumbent regimes

or they were vying for territorial self-determination or succession.

And the major finding of the research was that the nonviolent campaigns

had been twice as successful as the violent campaigns at achieving their objectives.

So the data has been updated through 2014 and the findings were almost exactly the same.

What we found through the research to be the most significant variable

in determining the outcomes of these campaigns was the size and the diversity of participation.

In the dataset, we found that the average nonviolent campaign attracted something like 11 times

the level of participants as the average violent campaign,

which makes sense because it's so much easier to participate in nonviolent resistance

compared to armed insurgencies.

The physical moral barriers to participation are much lower,

so young and old, elderly, abled body, disabled, lots of people can participate in nonviolent resistance

because there are so many ways to get involved, thousands probably at this point.

The risk also of targeting police and security forces with violence or perceived violence

is that they are much less likely to sympathize with the protesters when they're being attacked.

We've seen this in many cases and this tends to be a strategic advantage of nonviolent resistance,

whether it was in the Philippines in 1986 or in Ukraine during the Orange Revolution in Maidan.

You saw major defections by elements of the security forces

when they were faced with disciplined unarmed protesters.

We found that the average duration of a nonviolent campaign was three years.

The average duration for violent campaigns incidentally was nine years.

The challenge is just being able to maintain the focus in the long-term perspective

and be able to come up with ways to declare small victories

along the way to people to keep people engaged,

and not to escalate without being able to sustain that level of engagement.

So I think those are a few principles at least of what effective civil resistance has historically looked like

but what forms it will continue to take in Hong Kong is to be seen.