how would California and Texas stay independent

hi I have a really good idea for a time line and I would like to know how California and Texas could stay independent. anyone have any good ideas?
 
No mexican-american war in the 1840's. Instead us civil war breaks out in 1845. Meanwhile California and Texas gain independance and stay thar way. By time us civil war over focus on reconstruction and ex slaves and not expanding. California and Texas have 15 years time to think ofnthemselves as independant countries
 
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