The 4,000 officers on Pittsburgh's streets for the G-20 conference late next month would represent the largest armed force ready for action in these parts since 8,000 state militiamen -- Pennsylvania's entire military force -- marched on Homestead during the steelworkers strike in July 1892.

Before that, militia regiments were brought into Pittsburgh during the violent railroad strike of 1877, and they marched into Western Pennsylvania to squash the Whiskey Rebellion of 1794. Pittsburgh was essentially founded with a similar show of force late in 1758, when Gen. John Forbes, a Scotsman, commanded an army so large it persuaded the French to burn Fort Duquesne to the ground and flee.

There may be other examples, but they don't come immediately to mind as I try to envision what 4,000 cops, some of them undercover, will look like in our small Downtown. It surely seems as if this show of force is out of proportion to the threat, with nothing on the horizon that would match the historic crises of the past 250 years.

Overly prepared may be good, though, provided that over-preparation does not presage over-reaction.

A year and a half ago, I tried to get hundreds of people out of the David L. Lawrence Convention Center after a train filled with chlorine gas derailed just outside. It was just a drill, a "tabletop exercise" in the FBI Citizens' Academy on the South Side. We were "working for a safer tomorrow." Trouble was we weren't ready for the present.

As I recall, by the time the exercise ended, the death toll was in double digits and injuries cleared the century mark.

I was second in command. When the real FBI agents praised us afterward for not losing our cool as this fictional hell descended on the Golden Triangle, I couldn't help but wonder how low the bar was set for the likes of us. Evidently, not using all the body bags equals a good job for the amateurs.

I don't expect any such catastrophes on Sept. 24 and 25. Though some anarchists are expected, most protesters will be no more violent than an angry letter to the editor. Either way, local, state and federal law enforcement will be far better trained than the citizens who were thrown into the fray after a half-hour Power-Point prep. Strategists will have scouted and prepared the terrain, will know its weaknesses and blind spots, and will keep anything funny from coming up or down the Allegheny River.

I can remember from our little exercise, however, how quickly things can escalate when the shouting starts -- and that's just among people on the same side. Some want to jump the chain of command. Some make snap, independent decisions that go awry. It's not easy duty.

Care must be taken to ensure space is made for citizens to have their rightful say. That's important because the minor inconveniences of this two-day conference are less worrisome than the meat of the conference itself. The circuitous routes we may take to work and the classes and exhibition hockey game that will be postponed -- big whoop.

The switch from President George Bush to President Barack Obama has been universally seen as dramatic, but this much hasn't changed: The American economy is still based on filling our cars with imported gasoline so we can drive to the mall to buy Asian goods so foreigners can loan us back the dollars to finance two wars on the other side of the world while we sink further in debt.

So here are two questions world leaders likely will ask each other when the doors slam shut in the big rooms at the convention center: "How long can we expect this American economic model to last? And do we really want to keep loaning money to people who doubled U.S. government debt since 2001 and seem poised to double down again in the next decade?"

We in Pittsburgh are focused on the ancillary problems of the G-20 conference because it's here and we have to be. But after it's over, and delegates and journalists and protesters scatter back across the Earth, we and the rest of America may find that the real scary stuff lies ahead.