But, those conditions ended, in the mid-1970's, precisely because the economic expansion no longer created the sufficiently rising profits to facilitate the rising payments of interest. Interest rates rose, but the mass of interest grew more slowly than before, because the amount of profit grew more slowly, as capital accumulation slowed, and more of that profit was required for capital accumulation/profit of enterprise, leaving less for interest payments, rents and taxes. Capital was overproduced relative to labour supply/social working-day, so relative wages rose, relative profits fell.
In the 1950's and 60's, it was not that interest rates/dividend yields rose, as the basis of the ruling class revenues rising, on the contrary, interest rates and dividend yields were falling. The increased revenues came from a rapidly growing mass of profit, as capital expanded rapidly, during the post-war, long-wave uptrend. Similarly, in the mid-60's, and through to the mid-80's, interest rates rose, precisely because capital grew faster than labour supply/social working-day. Wage share/relative wages rose. Workers used those higher wages to demand more wage goods, and some of what had previously been luxury goods, as Marx describes in Capital II, and elsewhere, always happens in these conditions.
Competition, then, forced firms to respond to that higher demand, for fear of missing out, and losing market share. As Marx pointed out in response to Ricardo, capital does not need higher rates of profits or prices to get it to do that, competition forces it to do so, even as the consequence is a lower rate of profit, because, the alternative if to lose out in the competitive struggle.
“... the extension of cultivation to larger areas — aside from the case just mentioned, in which recourse must be had to soil inferior than that cultivated hitherto — to the various kinds of soil from A to D, thus, for instance, the cultivation of larger tracts of B and C does not by any means presuppose a previous rise in grain prices any more than the preceding annual expansion of cotton spinning, for instance, requires a constant rise in yarn prices. Although considerable rise or fall in market-prices affects the volume of production, regardless of it there is in agriculture (just as in all other capitalistically operated lines of production) nevertheless a continuous relative over-production, in itself identical with accumulation, even at those average prices whose level has neither a retarding nor exceptionally stimulating effect on production.The demand increases constantly, and, in anticipation of this new capital is continually invested in new land, although this varies with the circumstances for different agricultural products. It is the formation of new capitals which in itself brings this about. But so far as the individual capitalist is concerned, he measures the volume of his production by that of his available capital, to the extent that he can still control it himself. His aim is to capture as big a portion as possible of the market. Should there be any over-production, he will not take the blame upon himself, but places it upon his competitors.”
Marx explains the process, also, in Value, Price & Profit, where he shows that a rise in relative wages, does not cause higher prices/inflation, but shifts capital towards the production of wage goods, and away from the production of luxury goods. To increase supply of wage goods, firms employed more workers, bought more machines, materials and premises, even though those higher relative wages meant lower relative profits. The higher demand for all these Department I (producer) goods, also, then, meant Department I had to increase its output, accumulate additional capital. Capital, as a whole, therefore, was forced to expand, but, in conditions where its expansion, now, created an even greater relative shortage of labour, rising wage share and squeezed profits. A greater proportion of those profits, therefore, now had to go to funding capital accumulation, rather than the payment of interest/dividends. So, interest rates rose.
By the mid 1970's, the ruling-class and its media were complaining about the problem of “crowding out”. That is, because the government could borrow money-capital in the market and pay whatever lenders demanded, the consequence, as the supply of money-capital fell, was that firms faced interest rates that precluded their own expansion. The increased liquidity/supply of money tokens and credit, in this period, did not lead to lower interest rates – precisely because money tokens are not money, and money is not money-capital – but led, instead, to rising commodity price inflation, as output failed to grow proportionate to the expansion of liquidity.