This is somewhat an educational psychology question. A person's brain learns history by attaching new information to preexisting knowledge. If someone has a lot of preexisting knowledge, they are more easily absorb new information and incorporate it into their web of knowledge. Then when the time comes, it is easier for this person to recall information or use it in a new way. If someone has less preexisting knowledge, more details float around, unattached to anything, and they eventually dissipate. This is normal for humans. It does not make you dumb.

At the same time, you want to be trying to consume information that is in your personal "zone of proximal development," meaning that you are aiming to read stuff that is neither too basic nor too advanced. If you go into an academic library and just pull a random, thick war history book off the shelf with absolutely no clue what it is about, this book will simply be too hard for you to understand. Though you can easily read the words of the book, the material won't stick. You won't take very much away from the book. The methods, materials, sources, questions, and terms the author uses simply won't mean anything to you. That isn't because you're dumb; it's because the material was too advanced to stick to what you already know. Your husband on the other hand might be able to digest some or most of that information and stick it into his mental framework, not because he is smarter than you but because he has more places where the details connect to stuff he already knows.

So the most important thing to increase understanding is that you read stuff or listen to podcasts that are interesting for you. If you're reading a book for fun, and you just literally can't even, switch to something else! No problem. Being curious and having fun is the most important thing. You're not competing with others. The more you read, the more your preexisting knowledge will develop, which will help you unlock more of the materials you consume in the future. It is an exponential growth situation where it will be agonizingly slow at first, then a little faster, then a little faster, then faster, then A LOT fast, etc.

Also, if you don't like learning about war, learn about some other aspect of history. Learn about normal people. Or food. Or popular culture. Or trade networks. Or sex. Or whatever. War is not the only thing that is important in history. And guess what, you'll pretty quickly be able to turn the tables on your husband when you start talking about something he's never heard about, like Merchant's theory about how gendered conceptions of the environment helped justify the exploitation of the Earth's resources. He'll be like..."what are you talking about? I guess I'm just not as intelligent as the people around me." And then you'll teach him about it, and you'll have a little debate, and it'll be fun!

There are strategies you can utilize to retain more information during this learning process. Note taking is essential. Write down your thoughts on books and podcasts. What was the main point of the material? Write a three sentence summary of something you read or watched. The act of distilling information into digestible pieces written in your own words helps your brain remember stuff. This is true across all subject areas. While taking notes, also try to make connections to other things you've read or listened to. You asked about trying to understand how one thing in one place affected another place. Your notes are the perfect place to brainstorm these connections. The act of making connections helps attach new knowledge to your existing knowledge, which helps you retain more of it. I literally have hundreds and hundreds of pages of notes that I've taken over the years, so if I need to check something, I can just ctrl + f my notes and find the author or the topics I need. Also, while reading, I underline things I think are interesting in the book. I write notes to my future self in the margins to remind future me what present me is thinking or wondering. At the end of chapters, I write a one sentence summary of the chapter, if I think it is particularly important.

Regarding your specific questions, maybe create your own little hand-written timelines in your notes. These don't have to be the most elaborate timelines, just something to help you periodize and track details. Eventually, your brain will do this on its own, and you won't need to write it out.

As you read more, you'll also start to notice how historians are talking and debating with each other. I always approach reading or listening to podcasts by seeking the central thesis of their argument. What is the point of this text? What is the author trying to convince me of? Then I can compare it to what other historians have said. For example, what does this author say that is different from what this other person said? Or...what is the focus of this historian, and why does she focus on that? What is unique about her approach? What questions does she try to answer that are different from what another person investigated?

Memorizing sequences of dates and effects will eventually fall away, and you will be able to "see" the general scope of historical events in your brain. I can move around spatially and chronologically to different areas of my mental map/timeline to imagine roughly what was going on at any one time, and how those are connected to other events. For me, I also have this other weird mental overlay on my historical mental map. I can sort of "see" different historians' interpretations and ideas about history...kind of integrated into my map. Like my notes are on my mental map too. I can also picture different historical documents that I've read that relate to different movements in history, helping me envision what people were thinking and doing.

Of course, this took me decades to create, but it happened just because I like reading history. Curiosity is key, which you already clearly have. Just keep finding stuff you like, trying new things, and embracing your own personal journey.

First of all, history is as complicated as life multiplied by the number of lifetimes and increased due to the problems with (often limited) sources. It is neither shameful nor a bad thing if you feel overwhelmed by grappling with a good understanding of historical events.

My perspective on this is somewhat shaped by constructivism and others might strongly disagree but understanding a historical event (or even era) actually means getting a more or less specific imagination and appreciation of what may have happened. The more this understanding is supported by sources and science the better - but perfection will be unattainable even in modern history and ever more for eras longer in the past.

Take for example something as well documented as the Cuba Crisis during the Kennedy era. While you can get a lot of information on that, the political thinking, the true reasons for much of what was happening will be up for debate and depend on interpretation. Therefore the idea of just memorising the facts is in a way kind of ahistorical.

That being said, accepted facts (or rather: well documented impressions provided with reliable and available sources) may form a decent base of understanding for a given historical event. But please don’t forget to take ANY “historical fact” with a healthy amount (not more not less) of scepticism.

Now after this rambling I’d like to get to the heart of Your questions. If you have a hard time memorising details you should focus on the areas that are the most interesting to you and build the facts around these. If, for example, you are interested in the Triumvirate of Augustus and Co. you start with that. The You can kind of build around that. You may need to “gray out” some areas because no one can keep everything that happened in - say 1779 or 82 AD - straight. Actually, we don’t even KNOW everything that happened in these years. I would therefore always give the advice I was given:

Focus. Focus on your “Erkenntnisinteresse” (scientific interest or leading question) and investigate (and try to remember) the facts which you feel useful to enhance your research into that.