To best answer this question you have to define what you mean by "truly absorb". The United Kingdom was formed in 1707 with the joining of Scotland and England under the Acts of Union; Ireland officially joined the United Kingdom with the Acts of Union of 1800. Scotland has its own history of Home Rule debates, as well as uprisings.

The prime distinction between Ireland and Scotland would be religion, though there are many others: Ireland's Catholicism led to various points of tension. Economics of Ireland's land system furthered conflict between the two nations. There are a lot of ways to go about discussing this issue but we need to first define "truly absorb", at least for me to be able to help tonight.

In the case of Scotland, doesn't this have somewhat to do with the ascension of James Stewart (James the 6th of Scotland) to the English throne (becoming James the 1st of England)? Or was Scotland considerably "absorbed" by England before this?