That's a good question, MM. Before explicitly suggesting resources, here's a bit of my perspective. I don't mean to get off topic and I certainly don't mean to violate forum rules, but one's perspectives will color their method of investigation.
It seems to me that almost all theological movements morph over time, Wesleyan theology included. As an illustration, the "traditional view" that Second Temple Judaism avoided adopting Hellenistic features was convincingly overturned by Martin Hengel. 
Judaism and Hellenism: Studies in Their Encounter in Palestine during the Early Hellenistic Period
When I started in my education, many folks thought the traditional view was unassailable. So, when I search for stuff like this, I'm explicitly looking for books that show how it has changed.
Also, it's interesting to have watched the practice of Wesleyan theology morph even over my brief lifetime. I know a pastor who asserts that he's a dyed-in-the-wool traditional Wesleyan, but I'm pretty John Wesley would not recognize the practice of his theology.
So, I did a little search in my library, using AI to assist asking about the history of Wesleyan theology. One of the books that came up most often is the Religious and Theological Abstracts. You may not own many of the articles it points to, but it gives you an idea of some of the thinking that has been done on that topic.
Unfortunately, some of the Wesleyan systematic theologies I have seem to underemphasize how history has colored their writing. But I did find a few things that might be helpful:
The Dictionary of Christianity in America has a short article that suggests there have been changes, but neglects to give many details.
There's a helpful interview with Thomas Oden in Christian History Magazine 69. (Issue 114 might also have some helpful material.)
There are also hints of historical change in Oden's The Rebirth of Orthodoxy.
It's a little surprising that I don't have anything that really digs into the details of the history of Wesleyan thought. Most of my histories talk about the history of thought up to Wesley, then talk about groups and movements after Wesley.
But that's all I can find for now.
John Wesley was an Arminian Methodist. They have changed over time as most theological perspectives do with new generations. Look at the New apostolic reformation for example.. even in Calvinistic circles their doctrine change over time. I would look into Methodist theology and history.
Here is an excerpt from gotquestions.org that I hope helps
Thanks, Lew, this is very good. I picked up two resources from your post. Christian History 114 = $2 CAD & Methodist Theo for $4.00 CAD (I bought the Logos 6 Meth-Wesl Starter Library) saved a bunch and got more books. Love it.
You've given me some excellent leads and reading material.
HOWEVER, I got a quick question fore you…
Did Francis Asbury start Methodism or did he carry it on? You can tell I'm a newbie ;)
Once again, thanks!
Thanks, James! It sounds like it's a bit more involved than what I had originally thought it would be. It's not so "systematic" as following the trail of the doctrine of salvation from A-Z. Seems like there are some trails to follow which will eventuate to a deeper nuanced of that doctrine.
Thanks, again.
For question like Francis Ashbury, I like to start at to get a secular view before jumping into church histories. I know nothing about the Methodists other than isn't the Pietist movement essential background? Knowing Pietist Lutherans (a.k.a. Finnish Apostolic Lutherans), I was taught the Wesley's built off them.
Orthodox Bishop Alfeyev: "To be a theologian means to have experience of a personal encounter with God through prayer and worship."; Orthodox proverb: "We know where the Church is, we do not know where it is not."
Thanks, MJ. Reading the article now.
I'm no expert. I'm not even a Methodist. But I do know the aunts in "Arsenic and Old Lace" thought Mr. Hoskins was "a good Methodist".
As MJ said, the Wikipedia article is a good place to start and it gives credit to Francis Asbury for starting a denomination in the US. Coincidentally, I met Asbury University's men's soccer coach this past summer and I didn't realize the university and the seminary in Wilmore, KY have been completely separated for quite a while. 😃
I also know the denominational reconfiguring is a huge part of recent history in the United Methodist Church. But that's more a church polity thing (something the UMC has a storied history about; e.g., circuit riders the the old days and District Superintendents juggling pastors every couple years until fairly recently) rather than a history of Wesleyan thought kind of thing.
