The Bible and Koran both contain accounts of God killing unbelievers for idolatry, apostasy, and blasphemy. The Bible says God made the earth swallow up some Jews for doubting Moses.
Why does God not today do this- if indeed that god is never-changing?
Why doesn't God make the earth swallow up atheists and other unbelievers? Why doesn't God consume people with a glance?
Is it that God has changed? God has lost his power somewhere? Or this God- the god of monotheism, doesn't exist?
The answer exist for this. However, it is a bit involved. There are many parts to the answer. Among one of them is what the purpose of the Bible is since it clearly was not global conversion of all in all countries.
Ask yourself what the purpose of the ancient nation of Israel was, why was that nation God's people back then, why did God clearly indicate that that nation no longer was his chosen people!
The ancient nation of Israel's purpose was to demonstrate several matters, some of law, some of action, interaction. With God's interaction with this nation, God illustrated to all how he acts toward obedient people, disobedient people, how he protects them, how he punishes them - in regard to them obeying his law, or disobeying.
As we are told:
1 Corinthians 10:11 Now these things went on befalling them as examples, and they were written for a warning to us upon whom the ends of the systems of things have arrived.
Besides functioning as examples, all of the writings in the Bible we believe are inspired by God were given to Jews. Even in the NT which brought in a new covenant people of God consisting of Gentiles and Jews, only Jews were used to write these instructions for us.
It is hard to answer you since I do not know how well you know the Christian writings. But, the thing is that the promise of God is for a kingdom to be made of the entire earth, for all present day nations to be gathered under one rule, kingdom rule, a theocracy. The main ruler is going to be the glorified Christ. Below him a smaller but still large group of sub-king-priests shall be selected. This selection process has been going on since Jesus' death and resurrection.
Before the end of this world systems, nations, it was necessary to wait for the technological revolution. Without it, it would not become apparent that even with high technology at our finger tips, we still destroy the earth and wage destructive wars among ourselves, and therefore are not fit to rule ourselves. We are now at the very edge of time where God's rule shall be installed. Many shall mock this, but that is what is going to happen soon. Even now the nations are poised to begin the day of wrath.
18 The nations raged,
but your wrath came,
and the time for the dead to be judged,
and for rewarding your servants, the prophets and saints,
and those who fear your name,
both small and great,
and for destroying the destroyers of the earth.”
It is time for the nations to rage; it is time for the dead to be judged, for the wicked to be killed. Just look around yourself. Are the nations poised for war across the globe?!