if one thing makes inroads into another, it has a noticeable effect on the second thing, especially by reducing it, or influencing it :
Tax rises have made some inroads into the country's national debt.
if one thing makes inroads into another, it has a noticeable effect on the second thing, especially by reducing it, or influencing it :
Tax rises have made some inroads into the country's national debt.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005