What I've learned about marital problems from married people.
The spouses don't agree to fulfill their roles -- Wife doesn't know what a man wants and husband doesn't know what a woman would want.
As for topics of argument, I presume money and housework is the cause. Other causes include: living with in-laws, distant relationship - living in different counties,
Money: Husband greedy or spends too much on his parents/own brothers and sisters in cases where the wife doesn't work. If wife works arguments on who spends more on the household.
Housework: Wife wants to divide equally, husband doesn't really care about cleaning. Wife feels like a servant and unappreciated.
Both these problems have an influence on intimacy -- wife distance herself due to feeling unappreciated and stops taking care of her looks etc.. Husband on the other hand lacks loyalty, staring at other women inappropriately. etc.
Other complains from Women: He doesn't spend enough time with me. Never takes me out nor do we ever travel. He doesn't buy me presents. He humiliates me in front of people.
Other complains from men: I want more kids, She doesn't clean the house, she works too long hours.