I have recently been listening to the History of China podcast and was amazed at how often river combat was brought up. It appears as though southern China especially has a long and storied history of river warfare. (Modern term would be Brown-Water I think) So my question is why the Europeans did not have such a history? There are large rivers in Europe, such as the Rhine or Volga, why didn't the Europeans have as much River warfare? (Or at least as much storied warfare, I don't know of any European river battles.)
During the Age of Vikings especially one would think that investing in river defence would be a worthwhile endeavor, yet to my knowledge, this did not happen, at least, not on a large scale. Why is this? Did rulers not deem it cost-effective?
They did! The two leading examples from 9th and 10th Century England are London and Bath. The English urban centre at Lundenwic (about a mile upstream from the Roman city, near the modern site of Covent Garden) was attacked twice by Viking forces in 842 and in 850 in raids which, while devastating, were sufficiently irregular to most likely convince Mercian leaders that there was no need to heavily fortify the site itself. After the next "decennial" raid - on Winchester in 860 - was defeated in short order by the West Saxon army, it's easy to imagine a certain sense of security before the arrival of the Great Heathen Army in the late 860s. Alfred of Wessex reconstructed the Londinium defences in 886 and moved Lundenwic within the safety of those defences (likely a response to having had to defend the settlement from a Danish force there in 883), but also built an adjacent burh on the opposite bank. This South-work (modern-day Southwark) was linked to the London burh by a fortified bridge designed to impede unwanted river traffic from proceeding any further up the Thames. It's thought that Alfred may have got the idea from a childhood visit to Paris in 854-5 where he would have seen the newly-erected fortified Seine bridges built by Charles the Bald. Similar to the Thames defences at London, a discrepancy between the garrison size estimates from the Burghal Hidage and the known early medieval defensive circuit at Bath has led to the conclusion (Baker and Brookes, Beyond the Burghal Hidage, 2011) that Bath similarly had a fortified bridge designed to interdict unwanted travel up the River Avon.
A key factor, however, is that, at least from the 870s onwards, English naval strategy prioritised blue- rather than brown-water engagements, where the English warships were more effective fighting platforms. According to the Anglo-Saxon Chronicle:
They were almost twice as long as [the Danish ships], some had 60 oars, some more. They were both swifter and steadier and also higher than the others.
By virtue of their size and power, these ships were far more powerful in open sea warfare, but at the cost of manoeuvrability in shallower water. Their purpose was to interdict the Danes therefore before this became an issue, or at least to successfully divert and harass raiding fleets so that land-based forces could also respond. In 896, for example:
The King ordered a force to go thither (against a Danish force in the Solent) with nine of the new ships, and they blocked the estuary from the seaward end. Then the Danes went out against them with three ships, and three were on dry land further up the estuary; the men from them having gone up on land. Then the English captured two of those three ships at the entrance to the estuary, and killed the men, and the one ship escaped. On it also the men were killed except five. These got away because the ships of their opponents ran aground... That summer no fewer than twenty ships, men and all, perished along the South Coast.