There's two ways to read your question and I'm not certain which one you meant to ask, so I'll answer both. The first is: who ruled the land between ancient Greek cities? The second is: who ruled the parts of the Greek world that did not have city-states in them?

As to the first question, Greek city-states were not just cities. The countryside formed an essential part of them. In simplified terms, every Greek city-state (polis) consisted of a city (astu) and its surrounding agricultural hinterland (chora). The citizens of each polis usually had the exclusive right to own land within the chora. From their farms, vineyards and grazing lands, the community drew the majority of its food. Cities away from the coast would often rely on their own hinterland for all of their sustenance, since moving bulk goods over land was prohibitively difficult and expensive. The city and its hinterland were interdependent and inextricably bound together.

As the city-states of the Greek world emerged in the Archaic period, they began to assert the borders of their territory, which were often disputed. Many communities built important sanctuaries far away from the city, and one influential theory is that they did this deliberately to establish the border between their lands and those of their neighbours. Sometimes conflicts would break out over the control of borderland between two states, and these conflicts could drag on for centuries, flaring every now and then into open warfare. As the Greek states' resources grew, many of them would build networks of watchtowers and forts to control their whole territory rather than just the patches within sight of their city walls.

While smaller states might contol no more than a single valley or strip of coastal land, the bigger poleis could have a significant territory. Attika, for instance - the hinterland of Athens - was some 2,500km^2 or about the size of the modern state of Luxembourg. Such states may have had one main urban centre, but they would also have other towns and villages scattered throughout their chora, and these could be easily as large as a polis in their own right. The town of Acharnai, northwest of Athens, could muster some 4,000 hoplites in the late 5th century BC, which would have made it one of the largest poleis of the Greek mainland if it had been independent. This entire community and its land, however, was part of the polis of Athens. The Acharnians were citizens of Athens, could vote in the Athenian assembly, and so on. Other states had different arrangements: Sparta, for example, ruled a vast territory containing many towns that were effectively autonomous poleis, except that they were subjected to the Spartans and owed them military service. The so-called perioikoi ("those who live around") who inhabited these towns owned their own land and managed their own affairs, but their political rights were limited. It was only when many of them were liberated from Spartan rule in the 4th century BC that these communities began to form an independent buffer zone between Sparta and its larger neighbours.

In other words, the answer to this question is that it was the city-states themselves that ruled the countryside. It was very rare for a city to have no hinterland; usually this was only possible for trading posts that could rely on imported food paid for by other forms of income. The great majority of states held and jealously guarded their own agricultural land, and tried to expand it until they encountered rival states strong enough to dispute their claims. There was usually little to no unclaimed or wild land between city-states; at one point or another, one side would have claimed even the most marginal lands to graze its flocks.

The second question is just as interesting: what about those stretches of land in which there were no recognisable city-states? While the Peloponnese, Central Greece and the Aegean were thickly settled with city-states that ruled land in the way I just described, there were other regions that were considered less developed, especially in Western and Northern Greece. Who ruled the land in these more remote areas?

Traditionally, these regions have been described as the Greece of ethne, "tribes" or "peoples" - groups of people who spoke Greek and were culturally Greek but did not share the same level of urbanisation and the sophisticated political life that came with it. The Greeks saw them as more primitive versions of their own societies: people lived in smaller villages rather than nucleated settlements, maintained barbaric practices like piracy and carrying weapons in public, and were often organised in loose federations for their defence.

Nowadays, scholars mostly recognise that these villages were not so different from the cities that had emerged elsewhere. Many of them were poleis in all but name, and indeed, many of them would eventually be considered poleis by the Greeks themselves. We are talking about political communities on a smaller local scale and complexity, but recognisably similar in organisation; the "tribal" federation is simply a larger form of state formation within a region that did not have a single dominant centre. They were nevertheless often effective political entities; there is no better proof of this than the rise of the Aitolian League in the 3rd century BC, which remained one of the major players in Greek affairs for more than a century despite being based in a region with hardly any cities to speak of.

Other regions, though, were ruled by dynasts of varying degrees of stability, or by shifting alliances of ruling clans. We are poorly informed about many of these regions on the fringe of the Greek world until they suddenly leap into the limelight when Macedon conquers Greece. A lot of these regions were not quite considered Greek, precisely because they were not organised like poleis, but they left little room for enclaves of anarchy between the territories they controlled.