It is the wealth gained that can be measured by the change in the value of different asset classes in a specific economy and through asset class depreciation.
It can be gained when profits from a business are reinvested. It involves investment in physical fixed capital like factories, machines.
It also includes portfolio investment like the purchase of bonds, cryptocurrencies, shares, and investment in fixed assets, housing, buy to let etc.
One can gain through foreign direct investment, technological innovation, increase in human capital, new resources, and a higher level of investment savings and the earnings from profits or dividends from previous investments.
Capital is needed to make goods, machines, and factories and accumulated funds should exceed the necessity to overcome depreciation.
In general, to increase accumulation – the economy should enhance saving ratio, maintain proper banking and loan system, control corruption, and spend on infrastructure.
Marxist view finds capitalism prone to crisis and a means for capitalists to gain more wealth and dominance in society.