This is the easiest parajumble you will ever get in cat exam. The passage moves from the broader idea of "historical use of poisons" to a narrower idea of "biological weapons". 1 opens the paragraph. It then moves to biological weapons in 3. In 2 treaties are signed against the use poisoned weapons. In 4 there is additional info about the treaties, that they contained no means of control. Thus 1324 is the right sequence.