Objection 1. It would seem that strife is not a daughter of anger. For it is written (James 4:1): "Whence are wars and contentions? Are they not... from your concupiscences, which war in your members?" But anger is not in the concupiscible faculty. Therefore strife is a daughter, not of anger, but of concupiscence.
Objection 2. Further, it is written (Proverbs 28:25): "He that boasteth and puffeth up himself, stirreth up quarrels." Now strife is apparently the same as quarrel. Therefore it seems that strife is a daughter of pride or vainglory which makes a man boast and puff himself up.
Objection 3. Further, it is written (Proverbs 18:6): "The lips of a fool intermeddle with strife." Now folly differs from anger, for it is opposed, not to meekness, but to wisdom or prudence. Therefore strife is not a daughter of anger.
Objection 4. Further, it is written (Proverbs 10:12): "Hatred stirreth up strifes." But hatred arises from envy, according to Gregory (Moral. xxxi, 17). Therefore strife is not a daughter of anger, but of envy.
Objection 5. Further, it is written (Proverbs 17:19): "He that studieth discords, soweth [Vulgate: 'loveth'] quarrels." But discord is a daughter of vainglory, as stated above (Question 37, Article 2). Therefore strife is also.
On the contrary, Gregory says (Moral. xxxi, 17) that "anger gives rise to strife"; and it is written (Proverbs 15:18; 29:22): "A passionate man stirreth up strifes."
I answer that, As stated above (Article 1), strife denotes an antagonism extending to deeds, when one man designs to harm another. Now there are two ways in which one man may intend to harm another. On one way it is as though he intended absolutely the other's hurt, which in this case is the outcome of hatred, for the intention of hatred is directed to the hurt of one's enemy either openly or secretly. On another way a man intends to hurt another who knows and withstands his intention. This is what we mean by strife, and belongs properly to anger which is the desire of vengeance: for the angry man is not content to hurt secretly the object of his anger, he even wishes him to feel the hurt and know that what he suffers is in revenge for what he has done, as may be seen from what has been said above about the passion of anger (I-II, 46, 6, ad 2). Therefore, properly speaking, strife arises from anger.
Reply to Objection 1. As stated above (I-II, 25, 1,2), all the irascible passions arise from those of the concupiscible faculty, so that whatever is the immediate outcome of anger, arises also from concupiscence as from its first root.
Reply to Objection 2. Boasting and puffing up of self which are the result of anger or vainglory, are not the direct but the occasional cause of quarrels or strife, because, when a man resents another being preferred to him, his anger is aroused, and then his anger results in quarrel and strife.
Reply to Objection 3. Anger, as stated above (I-II, 48, 3) hinders the judgment of the reason, so that it bears a likeness to folly. Hence they have a common effect, since it is due to a defect in the reason that a man designs to hurt another inordinately.
Reply to Objection 4. Although strife sometimes arises from hatred, it is not the proper effect thereof, because when one man hates another it is beside his intention to hurt him in a quarrelsome and open manner, since sometimes he seeks to hurt him secretly. When, however, he sees himself prevailing, he endeavors to harm him with strife and quarrel. But to hurt a man in a quarrel is the proper effect of anger, for the reason given above.
Reply to Objection 5. Strifes give rise to hatred and discord in the hearts of those who are guilty of strife, and so he that "studies," i.e., intends to sow discord among others, causes them to quarrel among themselves. Even so any sin may command the act of another sin, by directing it to its own end. This does not, however, prove that strife is the daughter of vainglory properly and directly.
Source: Summa Theologica (New Advent)