So the king commanded Banaias the son of Joiada: and he went out and struck him, and he died.

And the king chargeth Benaiah son of Jehoiada, and he goeth out and falleth on him, and he dieth, and the kingdom is established in the hand of Solomon.

So the king gave orders to Benaiah, the son of Jehoiada; and he went out and, falling on him, put him to death. And Solomon's authority over the kingdom was complete.

And so the king commanded Benaiah, the son of Jehoiada. And going out, he struck him down, and he died.

And the kingdom was established - He had neither foes within nor without. He was either dreaded or loved universally. His own subjects were affectionately bound to him, and the surrounding nations did not think proper to make him their enemy.
As there are serious doubts relative to the dying charge of David as it relates to Shimei, most believing that, in opposition to his own oath, David desired that Solomon should put him to death; I shall here insert Dr. Kennicott's criticism on this part of the text: -
"David is here represented in our English version as finishing his life with giving a command to Solomon to kill Shimei, and to kill him on account of that very crime for which, as David here says, he had sworn to him by the Lord he would not put him to death. The behavior thus imputed to the king and prophet, and which would be justly censurable if true, should be examined very carefully as to the ground it stands upon; and when the passage is duly considered, I presume it will appear highly probable that an injury has been here done to this illustrious character. The point to which I now beg the reader's attention is this: That it is not uncommon in the Hebrew language to omit the negative in a second part of the sentence, and to consider it as repeated, when it has been once expressed, and is followed by the connecting particle. And thus on Isaiah 13:22 the late learned annotator says: 'The negative is repeated or referred to by the conjunction vau, as in many other places.' So also Isaiah 23:4. The necessity of so very considerable an alteration as inserting the particle Not, may be here confirmed by some other instances. Psalm 1:5 : The ungodly shall not stand in the judgment, Nor (the Hebrew is And, signifying and not) sinners in the congregation of the righteous. Psalm 9:18 : The needy shall not alway be forgotten, (and then the negative, understood as repeated by the conjunction, now dropped), the expectation of the poor shall (Not) perish for ever. Psalm 38:1 : O Lord, rebuke me not in thy wrath; Neither (And, for and not) chasten me in thy hot displeasure. Psalm 75:5 : Lift not up your horn on high, (and then the negative, understood as repeated by the conjunction, now dropped), speak (Not) with a stiff neck. Proverbs 24:12, (our version is this): Doth not he, that pondereth the heart consider it? and he that keepeth the soul, doth (Not) he know it? and shall (Not) he render to every man according to his works? And Proverbs 30:3 : I neither learned wisdom, Nor (And, for and not) have the knowledge of the holy. If then there are in fact many such instances, the question is, Whether the negative here, expressed in the former part of David's command, may not be understood as to be repeated in the latter part; and if this may be, a strong reason will be added why it should be, so interpreted. The passage will run thus: 'Behold, thou hast with thee Shimei, who cursed me - but I swore to him by the Lord, saying, I will not put thee to death by the sword. Now, therefore, hold him Not guiltless, (for thou art a wise man, and knowest what thou oughtest to do unto him), but bring Not down his hoar head to the grave with blood.' Now if the language itself will admit of this construction, the sense thus given to the sentence derives a very strong support from the context. For how did Solomon understand this charge? Did he kill Shimei in consequence of it? Certainly he did not; for after he had immediately commanded Joab to be slain, in obedience to his father, he sends for Shimei, and knowing that Shimei ought to be well watched, confines him to a particular spot in Jerusalem for the remainder of his life; 1-Kings 2:36-42. See also Job 23:17; Job 30:20; Job 31:20." This is the best mode of interpreting this text.

So the king commanded Benaiah the son of Jehoiada; which went out, and fell upon him, that he died. And the kingdom was (x) established in the hand of Solomon.
(x) Because all his enemies were destroyed.

So the king commanded Benaiah the son of Jehoiada, which went out,.... From the presence of the king, and took Shimei with him to the proper place of execution, it not being fitting to execute him before the king:
and fell upon him, that he died; put him to death by the sword:
and the kingdom was established in the hand of Solomon; Adonijah the usurper, and Joab the general of the army, who took on his side, being both put to death; and Abiathar the high priest deposed, who was in the same conspiracy; and Shimei, a dangerous and troublesome man, dispatched, there remained none to give any disturbance; so that he now sat easy and quiet on his throne, and things with respect to the civil government were on a firm and settled foundation.

the kingdom was established in the hand of Solomon--Now, by the death of Shimei, all the leaders of the rival factions had been cut off.

Solomon then ordered him to be executed by Benaiah. This punishment was also just. As Solomon had put Shimei's life in his own hand by imposing upon him confinement in Jerusalem, and Shimei had promised on oath to obey the king's command, the breach of his oath was a crime for which he had no excuse. There is no force at all in the excuses which some commentators adduce in his favour, founded upon the money which his salves had cost him, and the wish to recover possession of them, which was a right one in itself. If Shimei had wished to remain faithful to his oath, he might have informed the king of the flight of his slaves, have entreated the king that they might be brought back, and have awaited the king's decision; but he had no right thus lightly to break the promise given on oath. By the breach of his oath he had forfeited his life. And this is the first thing with which Solomon charges him, without his being able to offer any excuse; and it is not till afterwards that he adduces as a second fact in confirmation of the justice of his procedure, the wickedness that he practised towards his father. - The last clause, "and the kingdom was established by (בּיד) Solomon," is attached to the following chapter in the Cod. Al. of the lxx (in the Cod. Vat. it is wanting, or rather its place is supplied by a long interpolation), in the Vulgate, and in the Syriac; and indeed rightly so, as Thenius has shown, not merely because of the רק in 1-Kings 3:2, but also because of its form as a circumstantial clause, to which the following account (1-Kings 3:1.) is appended.