Is the God of the Old Testament different in the New Testament?

Read Isaiah 34.

Years ago, a man tried to tell me that the God of the Old Testament was a God of hate, while the God of the New Testament was  a God of love.  The error of that false statement is immediately evident to anyone who has ever actually read the Bible.  At the root of such heresy is the concept that God has changed His character over time.  Ridiculous.  "For I the LORD do not change." (Malachi 3:6)

When Jesus returns it will be a day of worldwide judgment upon the nations, especially on those who sought to annihilate Israel.  "For the LORD has a day of vengeance, a year of recompense for the cause of Zion" (v.8).  In this chapter, Edom is used as Exhibit A.  Israel's neighbor to the southeast was a constant enemy.

The descriptions in this chapter parallel with the Great Tribulation judgments as the seals are broken in Revelation.  These events then culminate in Revelation 19.  "From his mouth comes a sharp sword with which to strike down the nations, and he will rule them with a rod of iron.  He will tread the winepress of the fury of the wrath of God the Almighty." (Revelation 19:15)

Therefore, the time of earthly peace and blessing will only come after the returning Christ has decisively dealt with His enemies.

At the root of all current actions of man's inhumanity against others is sin.  It is not possible to negotiate that away.  There is only one cure in the universe for sin.

For now, we look forward to the day when Messiah will right every wrong and bring true justice to this world.  The Apostle Paul wrote: "If possible, so far as it depends on you, live peaceably with all.  Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, 'Vengeance is mine, I will repay, says the Lord."