Every system has a capacity of some kind. It must if it operates with mass/energy. There are limits to everything. There are limits to how tall we can actually grow, there are limits to how much stress we can sustain and there are limits to how much we can know at any one time. Look at any system long enough, and you will find an upper and lower bound (the limits) of its operation. For biological systems, there is also a range that is the most efficient (long distance runners know this as a marathon pace).
In terms of the economy of the United States, the limits to growth have historically been based on population (workers available), raw resources and demand (both internal and world demand).
As the nation expanded beyond the Thirteen Colonies (much to the detriment of Native Americans, already decimated by Old World diseases such as small pox, measles, typhus and measles), the central drive was an ideology of manifest destiny and the lust for land. Land was the primary resource for the US economy; land for farming, for animal husbandry and mining. Play any Civilization 1-5 and you'll understand the basics of natural resources (albeit, the game gives you nearly authoritarian control of the people).
The US Economy has historically grown at the rate of 5 or 6 percent (healthy) but also in the 2-3 percent range (anemic). Currently, the US is happy with 2-3 percent growth. In the last 30 years, the US economy accounts for roughly 1/4 of the total World GDP. In times of recession, the economy sheds wealth by -1 to -6%, sometimes in a single quarter.
This change in growth is the boom-bust of the economy. When the Fed took over control of the money supply, supposedly it was to streamline this cycle into a more predictable pattern. However, our rate of growth at the 2-3 rate, once called anemic, is now considered great.
The US economy has made major transitions in the repertoire of how it is made up, and each type imposes a natural limit on the maximum growth of the economy. The first is Agrarian- the type that Thomas Jefferson elevated to the ideal for a democracy where voters were the landed elite. The Industrial came next (remember, we still farm every piece of land possible to feed a growing population) and lasted until the 1950s, when the Service industry really was the prime driver of the economy (we still farmed and we still made stuff). Supposedly the 1990s was the Information age, and the Internet has done wondrous things in terms of innovation and efficiency (but at this time, we still farmed but no longer made stuff like we once did).
There were also societal changes that aided in these transitions; the end of slavery during the Civil War, the Suffrage Movement in the 1910s-1920s, the end of Jim Crow, the rise of Unions (democracy in the workplace) and the acceptance of Keynesian economic models for government policy in the 1930s-1960s (this list is not meant to be exhaustive- whole books are devoted just one of these listed items).
But for the whole, the economy was limited in some way; material resources and skilled labor. The country often went to war over resources (see the Spanish American war, which was just as much about bananas as it was about the Monroe doctrine) and invested heavily in public education (Thomas Jefferson created the first public university in Virginia- we had religious institutions that were private and served the elite since the Colonial period).
Most economists I've read assume that wealth is infinite (not Korten, whose argument is that growth cannot be infinite or we're all going extinct), that there is no endgame because wealth is a made up concept, essentially leverage to buy goods or services. Thus for some economists, wealth does not meet Kant's definition of reality (extension in space, duration in time) and is a psychological phenomena (the underlying reason so many economists are straying into behavioral psychology in their research).
One of the early limitation arguments was Malthus, who stipulated that world population growth (logarithmic) must outpace food production growth (linear). While he may be off by the years, due to mechanization and industrialization in the food supply- the earth does have a capacity, and in fact, multiple capacities, based on the standard of living by the population which inhabits it.
But my question, and one I've harbored for a long time, is what is the total capacity for the American economy?
I do not have an answer, but I do have some thoughts. A list of the current constraints on our economic growth follows;
1) Energy- as we deplete fossil fuels, this will become the next bottle neck
2) Destruction of the Industrial base- the inability to manufacture anything will severely limit the middle class to access the wealth of this nation.
3) Unemployment- when unemployment is high, it is a buyer's market, which depresses wages. Indeed, with huge growth rates for the top 1% of the nation's wealthy and stagnant real wage growth for everyone else since the 1970s, the average (or median if you prefer) American works harder for less, and thus, has less to spend.
4) Corporate Control of the Internet- with weak Net Neutrality regulation and corporate monopolies on access to the Internet, an important driver in today's information age, corporate censorship and manipulation of the Internet will severely limit growth.
5) Calcifying Wealth Pools- over the past 40 years, wealth has been allowed to accumulate for the top 1% in the nation (individuals, but mostly corporations) so that much of society's wealth is kept out of the economy. Rather than just use this wealth to create small loans, it is not utilized by our society. This is lost opportunity. The more that wealth is funneled to the top via our tax code and the natural calcification process of capitalism (monopolies will beat out competition every time- see the Gilded Age for the end game of capitalism), the less actual growth in our economy.
6) Destruction of the Environment- without a strong ecological system to support the world population, this will be a catastrophic event for the entirety of the human species, and a quick trip to Mad Max Land.
The above are all bottle necks to maximum capacity (not exhaustive). If someone is talking about the economy, and how to grow it, and they do not address these bottlenecks, you have a pretty good indication that said person is really a shill for the 1%-ers. Growth is not what they have in mind- all they care about is growth in their control of total wealth. (and yes, I know that Korten's main concern is changing the ideology of growth, or cowboy capitalism).