Capitalism, as a system, is inherently unstable.
Consider a closed economy. By closed we mean no money, and no resources, flow in or out of it. This is more general than it seems, since we are really talking net flow: We are thus talking about any economy where the flow of money in and the flow of money out are equal in magnitude. And any economy where the flow of resources in and the flow of resources out are equal in magnitude.
The economy consists of capital and labor. Profit is required by capital, in order to invest in greater production, that is, more capital. Thus capital must exploit labor. But, since the economy is closed, labor is capital's only market, except for itself. (Capital does not give its money, its demand, away to third parties.) But, capital cannot take a profit from itself. (Well, it can. But this is called taking a loss, when the expense borne by capital is greater than the return.) Indeed, capital cannot even break even, selling to itself, because of the costs of business, and because of the depreciation of capital.
Thus, capital must get in return more than it produces. (This is on two levels, real and financial.) So it takes a profit from labor. But what does this mean? The capitalist exploits labor twice. First, less is paid for labor than that labor produces. This produces a surplus of goods. This surplus is the profit of the capitalist. Some of this surplus is retained by the capitalist. Yachts, for instance. But yachts are an expense to the capitalist. And not all of this surplus can be retained. If it is, that is the break even point for the capitalist.
So the surplus must be sold, and it can only be sold to labor. This requires that the capitalist takes less from labor than it gives labor. But second, the capitalist takes more from labor than it gives labor in the first place as wages. But this results in an ever diminishing market, whereas the capitalist requires an ever expanding market.
Capital, in maximizing its profits, minimizes the return labor gets, even to the point where labor's return is negative. That is, each year labor is paid less, in real terms, than the year before. But this collapses the market for capital. This is the problem.
Indeed, for its market to grow, the capitalist must give labor (or some third party) some of the surplus of production. That is, capital must share its profits with labor. That is, labor must receive more than its costs. This will result in an expanding market, which is required for capital to grow.
Now with a closed real economy, the money supply can be changed. Thus an economy can be closed in real terms, (this is called Autarky,) yet 'open' in terms of money supply. That is, the money supply can be adjusted to favor either the financial or the real sector of the economy.
Keeping a fixed money supply is good for finance, but death to producers of real goods and services. Finance takes money out of the real economy. This is finance's cost, to the real economy, of doing business. This is its profit, as it redistributes demand in the real economy. Thus the money supply in the real economy decreases, and the real economy experiences deflation. But this means that, on average, the producers of real goods experience negative profit. Roughly, this means that, each year, over half of all non-financial businesses suffer losses.
Loaning money to the real economy does not reduce this over time, but rather increases it, because of the interest. Thus a period of deflation may be compensated for by finance loaning sufficient money to the real economy. However, it will subsequently be followed be an even greater period of deflation, as the loans come due. But this is superposed on the decline in production brought about by non-financial companies making negative profits. They will make money, and perhaps grow, while the money is being lent, but their markets will subsequently suffer an even greater contraction when loans come due, and can no longer be rolled over. Thus while there are fewer dollars, they are also pursuing fewer goods, which may even be inflationary, if production declines at a rate greater than the money supply in the real economy. Meanwhile, the supply of money in the financial sector increases, but has no outlet, except in bidding up asset prices. Of course, real assets, that is the producers of real goods, are increasingly overvalued, as their markets are increasingly undermined. Depending on the degree of indebtedness, the transition is more or less dramatic.
Therefore, the money supply must expand so that this profit, the money finance takes out, is zero. This requires that the money supply be expanded in the real economy, and not in the financial economy, which will merely aggravate the situation. Effectively, this means it must be done fiscally, and not monetarily. Finance must be taxed, and the money spent in the real economy.