What you have observed is the normal pattern within a kingdom.
When the kingdom is young many new players are allocated to it. Most quickly quit but a sizeable number get hooked on the game and the kingdom experiences a period of high activity and enthusiasm.
I recall that period in my own kingdom some two to three years ago with affection. Clans are able to recruit, people take an interest in the Kingdom's progress as well as in that of their town/s and their clan. Perhaps there is some diplomacy to achieve peace within the kingdom and co-operative play in KvK, KvKr and Fury. Clan chat is a sociable place to spend some time.
Subsequently the likely course for the kingdom is imperceptible decline. Few new players are allocated, clan numbers begin to fall rather than rise, high spending players who could not hack it in their previous kingdom run away and look to bully players in a much younger kingdom (before, almost always, running away again). Progress in towns slows.
Eventually it is the hard core players who remain and the kingdom gets called "dead".
Some few kingdoms follow a different course. Very high spending players group themselves together into the clans which can contest Jotunheim. I do not know what it may be like to inhabit one of these kingdoms without participating in the huge clan - perhaps it is fun, perhaps it is dull.
Were I a developer within plarium I might challenge the strategy of endlessly allocating servers to create new kingdoms. It seems to me that were there enough kingdoms for the number of active players (50 perhaps, or a hundred) then new players would continue to be allocated to all the kingdoms and a measure of vigour would thereby be encouraged. However an immediate consequence would be the need to clear away the inactive accounts and plarium, in common with all other developers, think it important to be able to claim a high number of accounts. Daft but, I suppose, just about understandable (if you can stomache what amounts to telling lies). Perhaps they also think that it is important to be able to point to many kingdoms, however many are "dead".
The poster above has not yet understood the game - no doubt led astray by experience of Clash of Clans. Having your town hit while a novice is irksome but also irrelevant. It is progress in knowledge, buildings, hero, shaman, hero/shaman equipment, Valkyries, skins, etc. which is relevant and all these things are invulnerable. Losing 50k silver turns out just not to matter. Moreover all experienced small or medium sized players keep a shield up 100% of the time save for a second or two when making attacks. OK it takes a beginner a short time to learn this and a little while to have the gold to do so. But joining a worthwhile clan gets the person both the information and the gold. Anyone playing "Vikings: War of Clans" who does not make joining a clan a priority needs to find another game.