paper we find that the star formation rate is proportional to the cloud mass above an extinction threshold of AK ≈ 0.8 mag, corresponding to a gas surface density threshold of Σgas ≈ 116M⊙ pc2. (or volume densities about 104 cm-3). In other words, once you have dense gas you have stars. The more dense gas you have, the more the stars you'll produce. Understanding star formation is understanding how nature transforms diffuse gas into dense gas. Easy.