Hello, I wrote about successful English strategies against the Vikings here.

It's useful to make a distinction between being effective raiders and being 'militarily dominant'. Viking strategies revolved around avoiding a fair fight as much as possible; Asser notes in his Vita Ælfredi that while the West Saxon army actually accounts itself fairly well in 871 in an exhausting series of battles against the Danes, their occasional defeats come about because of the need to expend vast amounts of manpower trying to fend off 'innumerable' raids in small skirmishes. As a result, Wessex was being 'bled dry' and was unable to bring their full army effectively against the Danes. Danish strategy depended heavily on manoeuvre and speed, and in raiding to tie down manpower, pick smaller forces off piecemeal, and create carnage before a response could be effected. The main strategic operation of the English burghal network was to severely limit this maneuverability, and instead allow English forces to react rapidly to incursions and force battle on their terms.

As already mentioned by u/BRIStoneman, Vikings were pirates and raiders and they focused on sea raids because their homeland, with complex coastlines and numerous island facilitated maritime operations, be it military or commercial. But is it true that they ruled the northern European seas? Well, not really. Although Norse warriors were able to raid the monasteries, with the best know example being that of the Lindisfarne in 793, it should be noted that Viking raids were often aimed at targets that would generate substantial spoils while at the same time were also relatively poorly defended, while significant trading centers were usually targeted by large and well organized military expeditions. What is interesting, Scandinavian raiders seemed to avoid the raiding activities to their close east, and according to the archaeological findings, their presence on the southern shore of the Baltic Sea was very small, even though these regions were well-developed and relatively densely populated by Eastern Germanic and Northern Slavic peoples.

Nortwestern Slavic people, such as Polabians, most notably Ranes, Veleti (Lutites) and Obotrites, inhabiting what is modern Mecklemburg-Vorpommern in Germany, as well as Pomeranians, inhabitants of what is Western Pomerania in Poland, seemed to at least match the military prowess and presence of the Scandinavians, what could have been a strong deterrent against prevalent raiding in these areas. Existence of large mercantile and production centers like Arkona, Wolin, Kołobrzeg, Wolgast or Garz that were present as early as 9th century also indicated that locals were able to successfully deter pirate and military activities of their neighbours, including Swedes and Danes. Although much more scarce that these relating the exploits of Scandinavians, there are sources (Adam of Bremen, Saxo Grammaticus) mentioning Slavic pirates, known in Polish historiography as chąśnicy [xɔ̃ɕnit͡sɨ](from Old Polish chąśba, meaning 'robbery') that maintained very strong presence in western part of the Baltic Sea, being essentially a local counterpart to Scandinavian vikings.

This does not mean, however, that the area was peaceful or Scandinavians were afraid of sailing there. Between 9th and 11th century Veleti and Obotrites were often fighting Danes. For example, Danish king Gotfred captured Veletic port Reric in 808, what incidentally gave rise to the importance of Danish Hedeby that conversely became a target of raiding itself, having been plundered around 990 and later in 1066. The expedition of Magnus the Good in 1040s managed to plunder settlements as far east as modern Usedom and Wolin but triggered immediate retaliation of Weleti, Obotrites and Pomeranians that ended with attacks on many Danish settlements, including Aarhus and Ribe. It should be noted though, that the enmity was not constant and Polabian and Pomeranian Slavs were known to join forces against common opponent, such as in case of successful raids against Hamburg in the first half of 9th century that forced Church to relocate local archbishopric from Hamburg to Bremen in 845.

Although some sources mention the Danish presence in the Western Baltic, they are generally vague. Adam of Bremen mentions the settlement of Jumne, often identified as semi-legendary Jomsborg present in Jomsvikingasaga or Fagrskinna and Vineta, located somewhere between modern Szczecin and Ribnitz (it is possible it was located on an island, now underwater due to the rising of the Baltic sea, as suggested by the map of Pomerania from 1618 where Lubinus locates the Vineta island a bit north of what is now Koserow, Germany). It is possible that these two settlements refer to a single place as both are said to be raided and destroyed by aforementioned Magnus the Good. Archaeological findings confirmed Scandinavian presence on Wolin island (close to Szczecin in northwestern Poland) although scarcity of artifacts and their 'civilian' character suggest that Scandinavians were most likely visiting merchants or compose a local minority, corroborating Slavic or Germanic origins of the settlements there.

It was only after the centralization of the Denmark under Valdemar I (i.e. after the commonly defined Viking Age) and his alliance with Henry the Lion of Saxony and Albrecht the Bear of Brandenburg when the Polabian Slavs were ultimately subjugated by Danes with Ranes surrendering Arkona in 1168. Pomeranian rulers from the House of Griffin were hesitant to accept the supremacy of either Germans or Poles tried to remain independent, but eventually they were vassalized by Canute VI in 1185. When Canute's successor, Valdemar II got into conflict with Henry of Schwerin, the latter managed to emerge victorious with the support of the Emperor Frederic II and as a result, all Slavic lands gained by Canute VI were passed to Brandenburg margraves.