From the unofficial NT Write page:

But ‘theocracy’, in a sense yet to be defined, is of course what is meant by ‘the kingdom of God’, which the synoptic gospels highlight at the central motif of Jesus’ public announcements and which the fourth gospel presupposes as his central theme (the first time we meet it in John it seems to be assumed that this is what Jesus is all about). We know from Josephus that the revolutionaries, in the last century before the disastrous Roman-Jewish war, took as their battle-cry the slogan ‘no king but God!’ Presumably they thought they knew how God would exercise that kingly rule. Probably they imagined themselves having some role as divine agents. But we should not doubt that ‘God’s kingdom’ denoted the long-awaited rule of Israel’s God on earth as in heaven. The widespread assumption today that ‘the kingdom of God’ denotes another realm altogether, for instance that of the ‘heaven’ to which God’s people might hope to go after their death, was not on the first-century agenda. When Jesus spoke about God’s kingdom, and taught his followers to pray that it would arrive ‘on earth as in heaven’, he was right in the middle of first-century Jewish theocratic aspirations.