You have read all thirteen chapters. Now it is time to thread the scattered lessons into one.
The Art of War handles different situations, and from beginning to end it says one thing. The side that calculates the cost of a fight wins.
兵者，國之大事，死生之地，存亡之道，不可不察也
bing zhe, guo zhi da shi, si sheng zhi di, cun wang zhi dao, bu ke bu cha ye
War is the great affair of a state. It is the ground of life and death, the road to survival or ruin, and it cannot go unexamined. (The Art of War, Laying Plans, translated directly)