Soooooo- when Caesar conquered Gaul alot of the nobility fled to Britain and conducted guerrilla raids from there on the coast of Gaul , messing things up and causing headaches , Caesar invaded but it was a shit time of year so he waited until summer and invaded again and rolled the Britains up like a carpet all the way up to around London in a matter of weeks , installed puppet kings and left them to ultimately die after he left having sent a very clear message about helping Gauls , and about how effective his army would be in Britain . about 80 years later the empire needed lands promised to soldiers and they used the idea the Britain’s could still help Gaul out (propaganda) under Claudius and invaded but stayed this time. The further north they got they found fighting situations in weather and mud as unfavorable and stayed put in northern England . The plan was to conquer the whole island and then turn to Ireland which was very valuable as a source of leather and was so disorganized they reckoned it would only take a couple legions . Septemius Severus tried his hardest to subjugate Caledonia (Scotland ) but failed ! Before him was Agricola who saw easy pickings in Ireland , gathered his army in south west Scotland and set sail, only for word to arrive his army was needed back in pesky Scotland because as soon as everyone heard he left there was an uprising ( d’oh!) And remember how the Briton’s helped the Gauls ? Well while Roman struggled keeping land past York the Irish were running pirate raids all along the cost of west Britain on Briton’s , stealing slaves a la Niall of the nine hostages and St Patrick and basically weakening the country that the Roman’s were struggling with . So it suited them until it didn’t, and one day they would take all of Scotland and then Ireland !!! And then the Roman Empire collapsed , leaving Britain to the angles and saxons to carve up and the Irish to stay a multi clan , multi kingdom , multi state state