The relevance of obligations

I decided to re-read the epilogue, hoping to figure out exactly why Kerber is interested in a history of obligations. It certainly seems the case that Kerber believes that a history of women's obligations is a more informative way to explain the story of women's political autonomy and changing citizenship, than say simply a history of rights. On page 309 she writes that "I hope that this book has persuaded its readers that the basic obligations of citizenship have always been demanded of women; it is the forms and objects of that demand that have varied over time." I'm not sure if Kerber throws out an explicit and cohesive definition of obligation, if she did I certainly passed it over without notice. However, I think filling in this quote with a more clear understanding of what obligations are would really flesh out the history of women's obligations.
After some thinking on the basic conceptual difference between rights and obligations, it seems that obligations require and thus imply a set of abilities or autonomous means for action. This is distinct from rights insofar as rights merely offer avenues to express autonomy, they don't ever have to be actualized. Of course, this is probably more speculation on my part I haven't done much digging into he history of the definition of rights and obligations. Thus while women may have always had the obligations of citizenship, the political advancements over the course of 200 years have let them better express the autonomy they have always had access too. Therefore, a history of obligations would offer more insight into the ways women can and have expressed their autonomy more so than a history of only rights. But, this is all most just speculation, I would totally retract these ideas if presented with some badass evidence to say otherwise.