To discover what's responsible for a bull market, all we need to do is answer a couple of simple questions. In other words, when demand for a stock exceeds supply of a stock, the price will rise. It's simple economics. With that in mind, let's ask ourselves what the buyers use to purchase a stock. This time the answer is even more obvious.
Liquidity is the necessary lubricant of a healthy bull market.
Without it, markets can crumble no matter how good the fundamentals may appear. With it, the market can roar ahead because the financial system is awash in funds. To prove the point, let's examine the chart below. So the point is clear. Liquidity is the key force behind the stock market.