A fire doesn’t have to start with a flare. But two gases are in the equation and their abundance and ratios affect the intensity of the burning.
One is oxygen, or an oxidizing gas (chlorine is another oxidizer). The other gas is the fuel. With the exception of metal, just about any flaming fire is a gas that is burning. This is true of liquid fuel like oil or solid fuel like wood or paper. Prior to ignition, the fuel has to be heated to a point where a flammable gas is evolved. In liquid fuels, this means that the fuel must be at its flash point - the temperature at which flammable vapors are evolved. For gasoline, it is about minus 49 degrees Fahrenheit. For fuel oil (diesel fuel), it is over 100 degrees Fahrenheit. For solid fuels, the heat must be sufficient to pyrolytically decompose the material to a flammable gas. This is why when wood burns, you have a visible flame until it burns down to just the coals. At that point, the material that can be gasified and produce a visible flame is gone, but the remaining carbon is still oxidizing, burning, and giving off heat - just not a flame.
When something is first heated to the ignition temperature, the flammable gases and oxygen are at their maximum abundance. Whatever external heat source is applied to the fuel is causing it to give off gases that ignite when they hit the ignition temperature for that particular fuel. These gases ignite and burn rapidly. If this ignition stage fire produces enough heat to then cause the fuel to continue to give off flammable gas, the combustion is self-sustaining. If it is not, the fire will go out. Usually with solid fuel fires, combustion starts slowly and gradually increases as the the fuel temperature increases, reaching a vigorous free-burning stage. As the fuel is consumed, the flame dies down and eventually combustion stops as wither the fuel is all consumed, or the fire cannot produce sufficient heat to perpetuate the evolution of flammable gas.
Likewise at the moment of ignition, oxygen is at its maximum. It is consumed in the combustion. If the oxygen is not replaced - if the draft to the fire is restricted, the flame will diminish and maybe go out.
Then, typically, fires exist in a state of increasing starvation? If the oxygen around a fire were to be deliberately added at a steady rate, the fire would continue to flare?