The Holy verse says: "But, [on the contrary], We have provided good things for these [disbelievers] and their fathers until life was prolonged for them. Then do they not see that We set upon the land, reducing it from its borders? So it is they who will overcome?" (21:44)
The first explanation for this verse is that God is telling the disbelievers that they are enjoying the prosperity given to them by God. They enjoyed these favours for such a long time that they believe that they are their personal right and these privileges will never be taken away from them. God is telling them in this verse that that is not true. God can take away their prosperity because it is actually a gift from Him. To prove that God is telling them, don't you see that there are famines, epidemics, floods, earthquakes and other calamities. God is challenging them, if He decides to cause any of these disasters in a place will they be able to stop Him.
(See) here can either mean seeing by the eye, you have actually seen such disasters happen and no one can stop it. It can also mean knowledge about nations who lived before them who had been destroyed by such phenomena.
Just like the meaning conveyed in the following verses:
"Have you not considered how your Lord dealt with ‘Aad [With] Iram – who had lofty pillars, The likes of whom had never been created in the land? And [with] Thamud, who carved out the rocks in the valley? And [with] Pharaoh, owner of the stakes? – [All of] whom oppressed within the lands And increased therein the corruption. So your Lord poured upon them a scourge of punishment. Indeed, your Lord is in observation." (89:6-14)
This verse is revealed in Mecca (before immigration to Mediah). At that time they were fighting the Muslims in Mecca and torturing them to force them to return as disbelievers and leave Islam. The verse is NOT ordering the Muslims to steal lands, it is actually using historical facts known to the Arabs (the people of Mecca here) to prove that God does not leave the corruptors unpunished. The verse is telling them to look back in history and remember that all oppressors ended in destruction because actually the prosperity they were enjoying was a gift from God. Stories of old nations who were destroyed were known to the Arabs via the Jews at that time.
It is NOT a call for violence, it is actually a reminder to them to stop being aggressive against Islam, and not to be fooled by their current strength and power or else they will be punished and to prove that the verse reminded them of the old stories they know very well how fast land of oppression and injustice declined and vanished.