Given the number of civil wars which preceded it, why was this one "The" English Civil War?
England's population during the Wars of the Roses was under 2 million. During the period of The English Civil War, it was 4-5 million. The armies fielded by belligerents in both conflicts were about of the same size. Shouldn't they have been larger in the latter?
In the latter war, archers have given way to men bearing muskets. How much labor went into making a musket and did a shortage of muskets limit the size of the armies?
Why didn't the Scots or Irish "pile on" the conflict in an attempt to gain some form of political goal?
In responce to point four, the English civil war is seen as part of a system of conflicts known as 'the wars of the three kingdoms' (England, Scotland and Ireland). The chain of events is very complex, stemming from an intercision of political and religious motives and I reccommend pursuing independent reading.
In a simple timeline;
-A catholic irish rebellion raises religious tensions between the king and the English parliament, eventually this leads to a war between the king and the English parliament. Religiously sympathetic scottish Coventanders ally with the English parliment. The war ends with the kings surrender to a scottish army and he is turned over to the english.
-Political negotiations between the king, the scottish, the english army and the english parliament come to nothing. A failed revolt ends with the English army supreme over all others and the King is executed for treason.
-Excecution of the king galvanizes support in Scotland and Ireland, but these are militarily defeated by the English army.
To sum, during the descisive first civil war English and scottish co-religionists co-operate to limit the authority of their mutual king. *The war ends for a time.*Ireland is largely focussed on a civil war. Following this, scotland and ireland attempt to work with factions in England to gain advantage, but are militarily defeated in a series of wars by the reformed English army, which becomes the paramount political force in the British Isles.
Tl:dr: In response to point four; the Irish and scottish did pile in, but only (immediately) after the decisive english civil war ends and they are defeated in the subsequent wars.